diff --git a/lib/blocs/account/account_bloc.dart b/lib/blocs/account/account_bloc.dart
index 982e0e1..3c43162 100644
--- a/lib/blocs/account/account_bloc.dart
+++ b/lib/blocs/account/account_bloc.dart
@@ -4,7 +4,7 @@ import 'package:travel_mate/services/error_service.dart';
 import 'account_event.dart';
 import 'account_state.dart';
 import '../../repositories/account_repository.dart';
-import '../../data/models/account.dart';
+import '../../models/account.dart';
 
 class AccountBloc extends Bloc<AccountEvent, AccountState> { 
   final AccountRepository _repository;
diff --git a/lib/blocs/account/account_event.dart b/lib/blocs/account/account_event.dart
index 3b1b33d..0e63e7d 100644
--- a/lib/blocs/account/account_event.dart
+++ b/lib/blocs/account/account_event.dart
@@ -1,6 +1,6 @@
 import 'package:equatable/equatable.dart';
-import '../../data/models/account.dart';
-import '../../data/models/group_member.dart';
+import '../../models/account.dart';
+import '../../models/group_member.dart';
 
 abstract class AccountEvent extends Equatable {
   const AccountEvent();
diff --git a/lib/blocs/account/account_state.dart b/lib/blocs/account/account_state.dart
index 21db115..0257566 100644
--- a/lib/blocs/account/account_state.dart
+++ b/lib/blocs/account/account_state.dart
@@ -1,5 +1,5 @@
 import 'package:equatable/equatable.dart';
-import '../../data/models/account.dart';
+import '../../models/account.dart';
 
 abstract class AccountState extends Equatable {
   const AccountState();
diff --git a/lib/blocs/auth/auth_state.dart b/lib/blocs/auth/auth_state.dart
index 8806273..2897284 100644
--- a/lib/blocs/auth/auth_state.dart
+++ b/lib/blocs/auth/auth_state.dart
@@ -1,5 +1,5 @@
 import 'package:equatable/equatable.dart';
-import '../../data/models/user.dart';
+import '../../models/user.dart';
 
 abstract class AuthState extends Equatable {
   const AuthState();
diff --git a/lib/blocs/balance/balance_bloc.dart b/lib/blocs/balance/balance_bloc.dart
new file mode 100644
index 0000000..168ae00
--- /dev/null
+++ b/lib/blocs/balance/balance_bloc.dart
@@ -0,0 +1,81 @@
+import 'package:flutter_bloc/flutter_bloc.dart';
+import '../../repositories/balance_repository.dart';
+import '../../repositories/expense_repository.dart';
+import '../../services/balance_service.dart';
+import '../../services/error_service.dart';
+import 'balance_event.dart';
+import 'balance_state.dart';
+class BalanceBloc extends Bloc<BalanceEvent, BalanceState> {
+  final BalanceRepository _balanceRepository;
+  final BalanceService _balanceService;
+  final ErrorService _errorService;
+
+  BalanceBloc({
+    required BalanceRepository balanceRepository,
+    required ExpenseRepository expenseRepository,
+    BalanceService? balanceService,
+    ErrorService? errorService,
+  }) : _balanceRepository = balanceRepository,
+       _balanceService = balanceService ?? BalanceService(balanceRepository: balanceRepository, expenseRepository: expenseRepository),
+       _errorService = errorService ?? ErrorService(),
+       super(BalanceInitial()) {
+    on<LoadGroupBalance>(_onLoadGroupBalance);
+    on<RefreshBalance>(_onRefreshBalance);
+    on<MarkSettlementAsCompleted>(_onMarkSettlementAsCompleted);
+  }
+
+  Future<void> _onLoadGroupBalance(
+    LoadGroupBalance event,
+    Emitter<BalanceState> emit,
+  ) async {
+    try {
+      emit(BalanceLoading());
+      
+      final groupBalance = await _balanceRepository.calculateGroupBalance(event.groupId);
+      emit(BalanceLoaded(groupBalance));
+    } catch (e) {
+      _errorService.logError('BalanceBloc', 'Erreur chargement balance: $e');
+      emit(BalanceError(e.toString()));
+    }
+  }
+
+  Future<void> _onRefreshBalance(
+    RefreshBalance event,
+    Emitter<BalanceState> emit,
+  ) async {
+    try {
+      // Garde l'état actuel pendant le refresh si possible
+      if (state is! BalanceLoaded) {
+        emit(BalanceLoading());
+      }
+      
+      final groupBalance = await _balanceRepository.calculateGroupBalance(event.groupId);
+      emit(BalanceLoaded(groupBalance));
+    } catch (e) {
+      _errorService.logError('BalanceBloc', 'Erreur refresh balance: $e');
+      emit(BalanceError(e.toString()));
+    }
+  }
+
+  Future<void> _onMarkSettlementAsCompleted(
+    MarkSettlementAsCompleted event,
+    Emitter<BalanceState> emit,
+  ) async {
+    try {
+      await _balanceService.markSettlementAsCompleted(
+        groupId: event.groupId,
+        fromUserId: event.fromUserId,
+        toUserId: event.toUserId,
+        amount: event.amount,
+      );
+      
+      emit(const BalanceOperationSuccess('Règlement marqué comme effectué'));
+      
+      // Recharger la balance après le règlement
+      add(RefreshBalance(event.groupId));
+    } catch (e) {
+      _errorService.logError('BalanceBloc', 'Erreur mark settlement: $e');
+      emit(BalanceError(e.toString()));
+    }
+  }
+}
\ No newline at end of file
diff --git a/lib/blocs/balance/balance_event.dart b/lib/blocs/balance/balance_event.dart
new file mode 100644
index 0000000..d7c2c4d
--- /dev/null
+++ b/lib/blocs/balance/balance_event.dart
@@ -0,0 +1,43 @@
+import 'package:equatable/equatable.dart';
+
+abstract class BalanceEvent extends Equatable {
+  const BalanceEvent();
+
+  @override
+  List<Object?> get props => [];
+}
+
+class LoadGroupBalance extends BalanceEvent {
+  final String groupId;
+
+  const LoadGroupBalance(this.groupId);
+
+  @override
+  List<Object?> get props => [groupId];
+}
+
+class RefreshBalance extends BalanceEvent {
+  final String groupId;
+
+  const RefreshBalance(this.groupId);
+
+  @override
+  List<Object?> get props => [groupId];
+}
+
+class MarkSettlementAsCompleted extends BalanceEvent {
+  final String groupId;
+  final String fromUserId;
+  final String toUserId;
+  final double amount;
+
+  const MarkSettlementAsCompleted({
+    required this.groupId,
+    required this.fromUserId,
+    required this.toUserId,
+    required this.amount,
+  });
+
+  @override
+  List<Object?> get props => [groupId, fromUserId, toUserId, amount];
+}
\ No newline at end of file
diff --git a/lib/blocs/balance/balance_state.dart b/lib/blocs/balance/balance_state.dart
new file mode 100644
index 0000000..f79a956
--- /dev/null
+++ b/lib/blocs/balance/balance_state.dart
@@ -0,0 +1,40 @@
+import 'package:equatable/equatable.dart';
+import '../../models/group_balance.dart';
+
+abstract class BalanceState extends Equatable {
+  const BalanceState();
+
+  @override
+  List<Object?> get props => [];
+}
+
+class BalanceInitial extends BalanceState {}
+
+class BalanceLoading extends BalanceState {}
+
+class BalanceLoaded extends BalanceState {
+  final GroupBalance groupBalance;
+
+  const BalanceLoaded(this.groupBalance);
+
+  @override
+  List<Object?> get props => [groupBalance];
+}
+
+class BalanceOperationSuccess extends BalanceState {
+  final String message;
+
+  const BalanceOperationSuccess(this.message);
+
+  @override
+  List<Object?> get props => [message];
+}
+
+class BalanceError extends BalanceState {
+  final String message;
+
+  const BalanceError(this.message);
+
+  @override
+  List<Object?> get props => [message];
+}
\ No newline at end of file
diff --git a/lib/blocs/expense/expense_bloc.dart b/lib/blocs/expense/expense_bloc.dart
new file mode 100644
index 0000000..6fc7875
--- /dev/null
+++ b/lib/blocs/expense/expense_bloc.dart
@@ -0,0 +1,136 @@
+import 'dart:async';
+import 'package:flutter_bloc/flutter_bloc.dart';
+import '../../repositories/expense_repository.dart';
+import '../../services/expense_service.dart';
+import '../../services/error_service.dart';
+import 'expense_event.dart';
+import 'expense_state.dart';
+
+
+class ExpenseBloc extends Bloc<ExpenseEvent, ExpenseState> {
+  final ExpenseRepository _expenseRepository;
+  final ExpenseService _expenseService;
+  final ErrorService _errorService;
+  StreamSubscription? _expensesSubscription;
+
+  ExpenseBloc({
+    required ExpenseRepository expenseRepository,
+    ExpenseService? expenseService,
+    ErrorService? errorService,
+  }) : _expenseRepository = expenseRepository,
+       _expenseService = expenseService ?? ExpenseService(expenseRepository: expenseRepository),
+       _errorService = errorService ?? ErrorService(),
+       super(ExpenseInitial()) {
+    
+    on<LoadExpensesByGroup>(_onLoadExpensesByGroup);
+    on<ExpensesUpdated>(_onExpensesUpdated);
+    on<CreateExpense>(_onCreateExpense);
+    on<UpdateExpense>(_onUpdateExpense);
+    on<DeleteExpense>(_onDeleteExpense);
+    on<MarkSplitAsPaid>(_onMarkSplitAsPaid);
+    on<ArchiveExpense>(_onArchiveExpense);
+  }
+
+  Future<void> _onLoadExpensesByGroup(
+    LoadExpensesByGroup event,
+    Emitter<ExpenseState> emit,
+  ) async {
+    try {
+      emit(ExpenseLoading());
+      
+      await _expensesSubscription?.cancel();
+      
+      _expensesSubscription = _expenseRepository
+          .getExpensesStream(event.groupId)
+          .listen(
+            (expenses) => add(ExpensesUpdated(expenses)),
+            onError: (error) => add(ExpensesUpdated([], error: error.toString())),
+          );
+    } catch (e) {
+      _errorService.logError('ExpenseBloc', 'Erreur chargement expenses: $e');
+      emit(ExpenseError(e.toString()));
+    }
+  }
+
+  Future<void> _onExpensesUpdated(
+    ExpensesUpdated event,
+    Emitter<ExpenseState> emit,
+  ) async {
+    if (event.error != null) {
+      emit(ExpenseError(event.error!));
+    } else {
+      emit(ExpensesLoaded(expenses: event.expenses));
+    }
+  }
+
+  Future<void> _onCreateExpense(
+    CreateExpense event,
+    Emitter<ExpenseState> emit,
+  ) async {
+    try {
+      await _expenseService.createExpenseWithValidation(event.expense, event.receiptImage);
+      emit(const ExpenseOperationSuccess('Dépense créée avec succès'));
+    } catch (e) {
+      _errorService.logError('ExpenseBloc', 'Erreur création expense: $e');
+      emit(ExpenseError(e.toString()));
+    }
+  }
+
+  Future<void> _onUpdateExpense(
+    UpdateExpense event,
+    Emitter<ExpenseState> emit,
+  ) async {
+    try {
+      await _expenseService.updateExpenseWithValidation(event.expense, event.newReceiptImage);
+      emit(const ExpenseOperationSuccess('Dépense modifiée avec succès'));
+    } catch (e) {
+      _errorService.logError('ExpenseBloc', 'Erreur mise à jour expense: $e');
+      emit(ExpenseError(e.toString()));
+    }
+  }
+
+  Future<void> _onDeleteExpense(
+    DeleteExpense event,
+    Emitter<ExpenseState> emit,
+  ) async {
+    try {
+      await _expenseRepository.deleteExpense(event.expenseId);
+      emit(const ExpenseOperationSuccess('Dépense supprimée avec succès'));
+    } catch (e) {
+      _errorService.logError('ExpenseBloc', 'Erreur suppression expense: $e');
+      emit(ExpenseError(e.toString()));
+    }
+  }
+
+  Future<void> _onMarkSplitAsPaid(
+    MarkSplitAsPaid event,
+    Emitter<ExpenseState> emit,
+  ) async {
+    try {
+      await _expenseRepository.markSplitAsPaid(event.expenseId, event.userId);
+      emit(const ExpenseOperationSuccess('Paiement marqué comme effectué'));
+    } catch (e) {
+      _errorService.logError('ExpenseBloc', 'Erreur mark split paid: $e');
+      emit(ExpenseError(e.toString()));
+    }
+  }
+
+  Future<void> _onArchiveExpense(
+    ArchiveExpense event,
+    Emitter<ExpenseState> emit,
+  ) async {
+    try {
+      await _expenseRepository.archiveExpense(event.expenseId);
+      emit(const ExpenseOperationSuccess('Dépense archivée avec succès'));
+    } catch (e) {
+      _errorService.logError('ExpenseBloc', 'Erreur archivage expense: $e');
+      emit(ExpenseError(e.toString()));
+    }
+  }
+
+  @override
+  Future<void> close() {
+    _expensesSubscription?.cancel();
+    return super.close();
+  }
+}
\ No newline at end of file
diff --git a/lib/blocs/expense/expense_event.dart b/lib/blocs/expense/expense_event.dart
new file mode 100644
index 0000000..d04d253
--- /dev/null
+++ b/lib/blocs/expense/expense_event.dart
@@ -0,0 +1,87 @@
+import 'package:equatable/equatable.dart';
+import '../../models/expense.dart';
+import 'dart:io';
+
+abstract class ExpenseEvent extends Equatable {
+  const ExpenseEvent();
+
+  @override
+  List<Object?> get props => [];
+}
+
+class LoadExpensesByGroup extends ExpenseEvent {
+  final String groupId;
+
+  const LoadExpensesByGroup(this.groupId);
+
+  @override
+  List<Object?> get props => [groupId];
+}
+
+class CreateExpense extends ExpenseEvent {
+  final Expense expense;
+  final File? receiptImage;
+
+  const CreateExpense({
+    required this.expense,
+    this.receiptImage,
+  });
+
+  @override
+  List<Object?> get props => [expense, receiptImage];
+}
+
+class UpdateExpense extends ExpenseEvent {
+  final Expense expense;
+  final File? newReceiptImage;
+
+  const UpdateExpense({
+    required this.expense,
+    this.newReceiptImage,
+  });
+
+  @override
+  List<Object?> get props => [expense, newReceiptImage];
+}
+
+class DeleteExpense extends ExpenseEvent {
+  final String expenseId;
+
+  const DeleteExpense(this.expenseId);
+
+  @override
+  List<Object?> get props => [expenseId];
+}
+
+class MarkSplitAsPaid extends ExpenseEvent {
+  final String expenseId;
+  final String userId;
+
+  const MarkSplitAsPaid({
+    required this.expenseId,
+    required this.userId,
+  });
+
+  @override
+  List<Object?> get props => [expenseId, userId];
+}
+
+class ArchiveExpense extends ExpenseEvent {
+  final String expenseId;
+
+  const ArchiveExpense(this.expenseId);
+
+  @override
+  List<Object?> get props => [expenseId];
+}
+
+// Événement privé pour les mises à jour du stream
+class ExpensesUpdated extends ExpenseEvent {
+  final List<Expense> expenses;
+  final String? error;
+
+  const ExpensesUpdated(this.expenses, {this.error});
+
+  @override
+  List<Object?> get props => [expenses, error];
+}
diff --git a/lib/blocs/expense/expense_state.dart b/lib/blocs/expense/expense_state.dart
new file mode 100644
index 0000000..ca00940
--- /dev/null
+++ b/lib/blocs/expense/expense_state.dart
@@ -0,0 +1,44 @@
+import 'package:equatable/equatable.dart';
+import '../../models/expense.dart';
+
+abstract class ExpenseState extends Equatable {
+  const ExpenseState();
+
+  @override
+  List<Object?> get props => [];
+}
+
+class ExpenseInitial extends ExpenseState {}
+
+class ExpenseLoading extends ExpenseState {}
+
+class ExpensesLoaded extends ExpenseState {
+  final List<Expense> expenses;
+  final Map<String, double> exchangeRates;
+
+  const ExpensesLoaded({
+    required this.expenses,
+    this.exchangeRates = const {'EUR': 1.0, 'USD': 0.85, 'GBP': 1.15},
+  });
+
+  @override
+  List<Object?> get props => [expenses, exchangeRates];
+}
+
+class ExpenseOperationSuccess extends ExpenseState {
+  final String message;
+
+  const ExpenseOperationSuccess(this.message);
+
+  @override
+  List<Object?> get props => [message];
+}
+
+class ExpenseError extends ExpenseState {
+  final String message;
+
+  const ExpenseError(this.message);
+
+  @override
+  List<Object?> get props => [message];
+}
\ No newline at end of file
diff --git a/lib/blocs/group/group_bloc.dart b/lib/blocs/group/group_bloc.dart
index be1778c..b7e20ac 100644
--- a/lib/blocs/group/group_bloc.dart
+++ b/lib/blocs/group/group_bloc.dart
@@ -4,7 +4,7 @@ import 'package:travel_mate/services/error_service.dart';
 import 'group_event.dart';
 import 'group_state.dart';
 import '../../repositories/group_repository.dart';
-import '../../data/models/group.dart';
+import '../../models/group.dart';
 
 class GroupBloc extends Bloc<GroupEvent, GroupState> {
   final GroupRepository _repository;
diff --git a/lib/blocs/group/group_event.dart b/lib/blocs/group/group_event.dart
index 237893a..605344a 100644
--- a/lib/blocs/group/group_event.dart
+++ b/lib/blocs/group/group_event.dart
@@ -1,6 +1,6 @@
 import 'package:equatable/equatable.dart';
-import '../../data/models/group.dart';
-import '../../data/models/group_member.dart';
+import '../../models/group.dart';
+import '../../models/group_member.dart';
 
 abstract class GroupEvent extends Equatable {
   const GroupEvent();
diff --git a/lib/blocs/group/group_state.dart b/lib/blocs/group/group_state.dart
index ea122aa..488cf07 100644
--- a/lib/blocs/group/group_state.dart
+++ b/lib/blocs/group/group_state.dart
@@ -1,5 +1,5 @@
 import 'package:equatable/equatable.dart';
-import '../../data/models/group.dart';
+import '../../models/group.dart';
 
 abstract class GroupState extends Equatable {
   const GroupState();
diff --git a/lib/blocs/message/message_bloc.dart b/lib/blocs/message/message_bloc.dart
index 37eb016..59f9cec 100644
--- a/lib/blocs/message/message_bloc.dart
+++ b/lib/blocs/message/message_bloc.dart
@@ -1,6 +1,6 @@
 import 'dart:async';
 import 'package:flutter_bloc/flutter_bloc.dart';
-import '../../data/models/message.dart';
+import '../../models/message.dart';
 import '../../services/message_service.dart';
 import '../../repositories/message_repository.dart';
 import 'message_event.dart';
diff --git a/lib/blocs/message/message_state.dart b/lib/blocs/message/message_state.dart
index 597911e..5d6a89f 100644
--- a/lib/blocs/message/message_state.dart
+++ b/lib/blocs/message/message_state.dart
@@ -1,5 +1,5 @@
 import 'package:equatable/equatable.dart';
-import '../../data/models/message.dart';
+import '../../models/message.dart';
 
 abstract class MessageState extends Equatable {
   const MessageState();
diff --git a/lib/blocs/trip/trip_bloc.dart b/lib/blocs/trip/trip_bloc.dart
index f214190..61963b9 100644
--- a/lib/blocs/trip/trip_bloc.dart
+++ b/lib/blocs/trip/trip_bloc.dart
@@ -1,6 +1,6 @@
 import 'dart:async';
 import 'package:flutter_bloc/flutter_bloc.dart';
-import 'package:travel_mate/data/models/trip.dart';
+import 'package:travel_mate/models/trip.dart';
 import 'trip_event.dart';
 import 'trip_state.dart';
 import '../../repositories/trip_repository.dart';
diff --git a/lib/blocs/trip/trip_event.dart b/lib/blocs/trip/trip_event.dart
index 19b2eff..cda58a0 100644
--- a/lib/blocs/trip/trip_event.dart
+++ b/lib/blocs/trip/trip_event.dart
@@ -1,5 +1,5 @@
 import 'package:equatable/equatable.dart';
-import '../../data/models/trip.dart';
+import '../../models/trip.dart';
 
 abstract class TripEvent extends Equatable {
   const TripEvent();
diff --git a/lib/blocs/trip/trip_state.dart b/lib/blocs/trip/trip_state.dart
index 203707b..021bd79 100644
--- a/lib/blocs/trip/trip_state.dart
+++ b/lib/blocs/trip/trip_state.dart
@@ -1,5 +1,5 @@
 import 'package:equatable/equatable.dart';
-import '../../data/models/trip.dart';
+import '../../models/trip.dart';
 
 abstract class TripState extends Equatable {
   const TripState();
diff --git a/lib/components/account/account_content.dart b/lib/components/account/account_content.dart
index 9b170d5..8a530df 100644
--- a/lib/components/account/account_content.dart
+++ b/lib/components/account/account_content.dart
@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:travel_mate/blocs/user/user_bloc.dart';
-import '../../data/models/account.dart';
+import '../../models/account.dart';
 import '../../blocs/account/account_bloc.dart';
 import '../../blocs/account/account_event.dart';
 import '../../blocs/account/account_state.dart';
diff --git a/lib/components/account/add_expense_dialog.dart b/lib/components/account/add_expense_dialog.dart
index 4f00106..0d03254 100644
--- a/lib/components/account/add_expense_dialog.dart
+++ b/lib/components/account/add_expense_dialog.dart
@@ -3,12 +3,13 @@ import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:image_picker/image_picker.dart';
 import 'package:intl/intl.dart';
-import '../../blocs/account/account_bloc.dart';
-import '../../blocs/account/account_event.dart';
-import '../../blocs/account/account_state.dart';
+import 'package:travel_mate/models/expense_split.dart';
+import '../../blocs/expense/expense_bloc.dart';
+import '../../blocs/expense/expense_event.dart';
+import '../../blocs/expense/expense_state.dart';
 import '../../blocs/user/user_state.dart' as user_state;
-import '../../data/models/group.dart';
-import '../../data/models/expense.dart';
+import '../../models/group.dart';
+import '../../models/expense.dart';
 
 class AddExpenseDialog extends StatefulWidget {
   final Group group;
@@ -148,8 +149,8 @@ class _AddExpenseDialogState extends State<AddExpenseDialog> {
 
     try {
       // Convertir en EUR
-      final amountInEur = context.read<CountBloc>().state is ExpensesLoaded
-          ? (context.read<CountBloc>().state as ExpensesLoaded)
+      final amountInEur = context.read<ExpenseBloc>().state is ExpensesLoaded
+          ? (context.read<ExpenseBloc>().state as ExpensesLoaded)
               .exchangeRates[_selectedCurrency]! * amount
           : amount;
 
@@ -168,15 +169,16 @@ class _AddExpenseDialogState extends State<AddExpenseDialog> {
         splits: selectedSplits,
         date: _selectedDate,
         receiptUrl: widget.expenseToEdit?.receiptUrl,
+        createdAt: widget.expenseToEdit?.createdAt ?? DateTime.now(),
       );
 
       if (widget.expenseToEdit == null) {
-        context.read<CountBloc>().add(CreateExpense(
+        context.read<ExpenseBloc>().add(CreateExpense(
           expense: expense,
           receiptImage: _receiptImage,
         ));
       } else {
-        context.read<CountBloc>().add(UpdateExpense(
+        context.read<ExpenseBloc>().add(UpdateExpense(
           expense: expense,
           newReceiptImage: _receiptImage,
         ));
diff --git a/lib/components/account/balances_tab.dart b/lib/components/account/balances_tab.dart
index dfb556a..4fa5872 100644
--- a/lib/components/account/balances_tab.dart
+++ b/lib/components/account/balances_tab.dart
@@ -1,8 +1,8 @@
 import 'package:flutter/material.dart';
-import '../../data/models/balance.dart';
+import '../../models/user_balance.dart';
 
 class BalancesTab extends StatelessWidget {
-  final List<Balance> balances;
+  final List<UserBalance> balances;
 
   const BalancesTab({
     super.key,
@@ -27,7 +27,7 @@ class BalancesTab extends StatelessWidget {
     );
   }
 
-  Widget _buildBalanceCard(BuildContext context, Balance balance) {
+  Widget _buildBalanceCard(BuildContext context, UserBalance balance) {
     final isDark = Theme.of(context).brightness == Brightness.dark;
     
     Color balanceColor;
diff --git a/lib/components/account/expense_detail_dialog.dart b/lib/components/account/expense_detail_dialog.dart
index d1a30b2..e9390a4 100644
--- a/lib/components/account/expense_detail_dialog.dart
+++ b/lib/components/account/expense_detail_dialog.dart
@@ -1,12 +1,13 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:intl/intl.dart';
-import '../../blocs/account/account_bloc.dart';
-import '../../blocs/account/account_event.dart';
+import 'package:travel_mate/models/expense_split.dart';
+import '../../blocs/expense/expense_bloc.dart';
+import '../../blocs/expense/expense_event.dart';
 import '../../blocs/user/user_bloc.dart';
 import '../../blocs/user/user_state.dart' as user_state;
-import '../../data/models/expense.dart';
-import '../../data/models/group.dart';
+import '../../models/expense.dart';
+import '../../models/group.dart';
 import 'add_expense_dialog.dart';
 
 class ExpenseDetailDialog extends StatelessWidget {
@@ -267,8 +268,7 @@ class ExpenseDetailDialog extends StatelessWidget {
                 IconButton(
                   icon: const Icon(Icons.check_circle, color: Colors.green),
                   onPressed: () {
-                    context.read<CountBloc>().add(MarkSplitAsPaid(
-                      groupId: expense.groupId,
+                    context.read<ExpenseBloc>().add(MarkSplitAsPaid(
                       expenseId: expense.id,
                       userId: split.userId,
                     ));
@@ -287,7 +287,7 @@ class ExpenseDetailDialog extends StatelessWidget {
     showDialog(
       context: context,
       builder: (dialogContext) => BlocProvider.value(
-        value: context.read<CountBloc>(),
+        value: context.read<ExpenseBloc>(),
         child: AddExpenseDialog(
           group: group,
           currentUser: currentUser,
@@ -310,9 +310,8 @@ class ExpenseDetailDialog extends StatelessWidget {
           ),
           TextButton(
             onPressed: () {
-              context.read<CountBloc>().add(DeleteExpense(
-                groupId: expense.groupId,
-                expenseId: expense.id,
+              context.read<ExpenseBloc>().add(DeleteExpense(
+                expense.id,
               ));
               Navigator.of(dialogContext).pop();
               Navigator.of(context).pop();
@@ -338,9 +337,8 @@ class ExpenseDetailDialog extends StatelessWidget {
           ),
           TextButton(
             onPressed: () {
-              context.read<CountBloc>().add(ArchiveExpense(
-                groupId: expense.groupId,
-                expenseId: expense.id,
+              context.read<ExpenseBloc>().add(ArchiveExpense(
+                expense.id,
               ));
               Navigator.of(dialogContext).pop();
               Navigator.of(context).pop();
diff --git a/lib/components/account/expenses_tab.dart b/lib/components/account/expenses_tab.dart
index 870eed9..2270436 100644
--- a/lib/components/account/expenses_tab.dart
+++ b/lib/components/account/expenses_tab.dart
@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
-import '../../data/models/expense.dart';
-import '../../data/models/group.dart';
+import '../../models/expense.dart';
+import '../../models/group.dart';
 import 'expense_detail_dialog.dart';
 
 class ExpensesTab extends StatelessWidget {
diff --git a/lib/components/account/settlements_tab.dart b/lib/components/account/settlements_tab.dart
index 26de8f0..1cdeb65 100644
--- a/lib/components/account/settlements_tab.dart
+++ b/lib/components/account/settlements_tab.dart
@@ -1,5 +1,5 @@
 import 'package:flutter/material.dart';
-import '../../data/models/balance.dart';
+import '../../models/settlement.dart';
 
 class SettlementsTab extends StatelessWidget {
   final List<Settlement> settlements;
diff --git a/lib/components/group/chat_group_content.dart b/lib/components/group/chat_group_content.dart
index 043df55..7ca3219 100644
--- a/lib/components/group/chat_group_content.dart
+++ b/lib/components/group/chat_group_content.dart
@@ -5,8 +5,8 @@ import '../../blocs/user/user_state.dart' as user_state;
 import '../../blocs/message/message_bloc.dart';
 import '../../blocs/message/message_event.dart';
 import '../../blocs/message/message_state.dart';
-import '../../data/models/group.dart';
-import '../../data/models/message.dart';
+import '../../models/group.dart';
+import '../../models/message.dart';
 
 class ChatGroupContent extends StatefulWidget {
   final Group group;
diff --git a/lib/components/group/group_content.dart b/lib/components/group/group_content.dart
index dc77fb9..04344f1 100644
--- a/lib/components/group/group_content.dart
+++ b/lib/components/group/group_content.dart
@@ -7,7 +7,7 @@ import '../../blocs/user/user_state.dart' as user_state;
 import '../../blocs/group/group_bloc.dart';
 import '../../blocs/group/group_state.dart';
 import '../../blocs/group/group_event.dart';
-import '../../data/models/group.dart';
+import '../../models/group.dart';
 
 class GroupContent extends StatefulWidget {
   const GroupContent({super.key});
diff --git a/lib/components/home/create_trip_content.dart b/lib/components/home/create_trip_content.dart
index 15db114..cbd03c6 100644
--- a/lib/components/home/create_trip_content.dart
+++ b/lib/components/home/create_trip_content.dart
@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
-import 'package:travel_mate/data/models/trip.dart';
+import 'package:travel_mate/models/trip.dart';
 import 'package:travel_mate/services/error_service.dart';
 import '../../blocs/user/user_bloc.dart';
 import '../../blocs/user/user_state.dart' as user_state;
@@ -9,8 +9,8 @@ import '../../blocs/trip/trip_event.dart';
 import '../../blocs/trip/trip_state.dart';
 import '../../blocs/group/group_bloc.dart';
 import '../../blocs/group/group_event.dart';
-import '../../data/models/group.dart';
-import '../../data/models/group_member.dart';
+import '../../models/group.dart';
+import '../../models/group_member.dart';
 import '../../services/user_service.dart';
 import '../../repositories/group_repository.dart';
 
diff --git a/lib/components/home/home_content.dart b/lib/components/home/home_content.dart
index c5594b9..7391ba5 100644
--- a/lib/components/home/home_content.dart
+++ b/lib/components/home/home_content.dart
@@ -7,7 +7,7 @@ import '../../blocs/user/user_state.dart';
 import '../../blocs/trip/trip_bloc.dart';
 import '../../blocs/trip/trip_state.dart';
 import '../../blocs/trip/trip_event.dart';
-import '../../data/models/trip.dart';
+import '../../models/trip.dart';
 
 class HomeContent extends StatefulWidget {
   const HomeContent({super.key});
diff --git a/lib/components/home/show_trip_details_content.dart b/lib/components/home/show_trip_details_content.dart
index b730a9b..90d82cb 100644
--- a/lib/components/home/show_trip_details_content.dart
+++ b/lib/components/home/show_trip_details_content.dart
@@ -5,7 +5,7 @@ import 'package:travel_mate/blocs/group/group_event.dart';
 import 'package:travel_mate/blocs/trip/trip_bloc.dart';
 import 'package:travel_mate/blocs/trip/trip_event.dart';
 import 'package:travel_mate/components/home/create_trip_content.dart';
-import 'package:travel_mate/data/models/trip.dart';
+import 'package:travel_mate/models/trip.dart';
 
 class ShowTripDetailsContent extends StatefulWidget {
   final Trip trip;
diff --git a/lib/data/models/balance.dart b/lib/data/models/balance.dart
deleted file mode 100644
index 3f0bfcd..0000000
--- a/lib/data/models/balance.dart
+++ /dev/null
@@ -1,34 +0,0 @@
-class Balance {
-  final String userId;
-  final String userName;
-  final double totalPaid;
-  final double totalOwed;
-  final double balance;
-
-  Balance({
-    required this.userId,
-    required this.userName,
-    required this.totalPaid,
-    required this.totalOwed,
-  }) : balance = totalPaid - totalOwed;
-
-  bool get shouldReceive => balance > 0;
-  bool get shouldPay => balance < 0;
-  double get absoluteBalance => balance.abs();
-}
-
-class Settlement {
-  final String fromUserId;
-  final String fromUserName;
-  final String toUserId;
-  final String toUserName;
-  final double amount;
-
-  Settlement({
-    required this.fromUserId,
-    required this.fromUserName,
-    required this.toUserId,
-    required this.toUserName,
-    required this.amount,
-  });
-}
diff --git a/lib/data/models/expense.dart b/lib/data/models/expense.dart
deleted file mode 100644
index 65b8ba3..0000000
--- a/lib/data/models/expense.dart
+++ /dev/null
@@ -1,243 +0,0 @@
-import 'package:cloud_firestore/cloud_firestore.dart';
-import 'package:flutter/material.dart';
-
-enum ExpenseCategory {
-  restaurant,
-  transport,
-  accommodation,
-  activities,
-  shopping,
-  other,
-}
-
-enum ExpenseCurrency {
-  eur,
-  usd,
-  gbp,
-  jpy,
-  chf,
-  cad,
-  aud,
-}
-
-class ExpenseSplit {
-  final String userId;
-  final String userName;
-  final double amount;
-  final bool isPaid;
-
-  ExpenseSplit({
-    required this.userId,
-    required this.userName,
-    required this.amount,
-    this.isPaid = false,
-  });
-
-  Map<String, dynamic> toMap() {
-    return {
-      'userId': userId,
-      'userName': userName,
-      'amount': amount,
-      'isPaid': isPaid,
-    };
-  }
-
-  factory ExpenseSplit.fromMap(Map<String, dynamic> map) {
-    return ExpenseSplit(
-      userId: map['userId'] ?? '',
-      userName: map['userName'] ?? '',
-      amount: (map['amount'] ?? 0.0).toDouble(),
-      isPaid: map['isPaid'] ?? false,
-    );
-  }
-}
-
-class Expense {
-  final String id;
-  final String groupId;
-  final String description;
-  final double amount;
-  final ExpenseCurrency currency;
-  final double amountInEur;
-  final ExpenseCategory category;
-  final String paidById;
-  final String paidByName;
-  final List<ExpenseSplit> splits;
-  final String? receiptUrl;
-  final DateTime date;
-  final DateTime createdAt;
-  final bool isArchived;
-  final bool isEdited;
-  final DateTime? editedAt;
-
-  Expense({
-    this.id = '',
-    required this.groupId,
-    required this.description,
-    required this.amount,
-    required this.currency,
-    required this.amountInEur,
-    required this.category,
-    required this.paidById,
-    required this.paidByName,
-    required this.splits,
-    this.receiptUrl,
-    required this.date,
-    DateTime? createdAt,
-    this.isArchived = false,
-    this.isEdited = false,
-    this.editedAt,
-  }) : createdAt = createdAt ?? DateTime.now();
-
-  Map<String, dynamic> toMap() {
-    return {
-      'groupId': groupId,
-      'description': description,
-      'amount': amount,
-      'currency': currency.name,
-      'amountInEur': amountInEur,
-      'category': category.name,
-      'paidById': paidById,
-      'paidByName': paidByName,
-      'splits': splits.map((s) => s.toMap()).toList(),
-      'receiptUrl': receiptUrl,
-      'date': Timestamp.fromDate(date),
-      'createdAt': Timestamp.fromDate(createdAt),
-      'isArchived': isArchived,
-      'isEdited': isEdited,
-      'editedAt': editedAt != null ? Timestamp.fromDate(editedAt!) : null,
-    };
-  }
-
-  factory Expense.fromFirestore(DocumentSnapshot doc) {
-    final data = doc.data() as Map<String, dynamic>;
-    final editedAtTimestamp = data['editedAt'] as Timestamp?;
-    
-    return Expense(
-      id: doc.id,
-      groupId: data['groupId'] ?? '',
-      description: data['description'] ?? '',
-      amount: (data['amount'] ?? 0.0).toDouble(),
-      currency: ExpenseCurrency.values.firstWhere(
-        (e) => e.name == data['currency'],
-        orElse: () => ExpenseCurrency.eur,
-      ),
-      amountInEur: (data['amountInEur'] ?? 0.0).toDouble(),
-      category: ExpenseCategory.values.firstWhere(
-        (e) => e.name == data['category'],
-        orElse: () => ExpenseCategory.other,
-      ),
-      paidById: data['paidById'] ?? '',
-      paidByName: data['paidByName'] ?? '',
-      splits: (data['splits'] as List<dynamic>?)
-              ?.map((s) => ExpenseSplit.fromMap(s as Map<String, dynamic>))
-              .toList() ??
-          [],
-      receiptUrl: data['receiptUrl'],
-      date: (data['date'] as Timestamp?)?.toDate() ?? DateTime.now(),
-      createdAt: (data['createdAt'] as Timestamp?)?.toDate() ?? DateTime.now(),
-      isArchived: data['isArchived'] ?? false,
-      isEdited: data['isEdited'] ?? false,
-      editedAt: editedAtTimestamp?.toDate(),
-    );
-  }
-
-  Expense copyWith({
-    String? id,
-    String? groupId,
-    String? description,
-    double? amount,
-    ExpenseCurrency? currency,
-    double? amountInEur,
-    ExpenseCategory? category,
-    String? paidById,
-    String? paidByName,
-    List<ExpenseSplit>? splits,
-    String? receiptUrl,
-    DateTime? date,
-    DateTime? createdAt,
-    bool? isArchived,
-    bool? isEdited,
-    DateTime? editedAt,
-  }) {
-    return Expense(
-      id: id ?? this.id,
-      groupId: groupId ?? this.groupId,
-      description: description ?? this.description,
-      amount: amount ?? this.amount,
-      currency: currency ?? this.currency,
-      amountInEur: amountInEur ?? this.amountInEur,
-      category: category ?? this.category,
-      paidById: paidById ?? this.paidById,
-      paidByName: paidByName ?? this.paidByName,
-      splits: splits ?? this.splits,
-      receiptUrl: receiptUrl ?? this.receiptUrl,
-      date: date ?? this.date,
-      createdAt: createdAt ?? this.createdAt,
-      isArchived: isArchived ?? this.isArchived,
-      isEdited: isEdited ?? this.isEdited,
-      editedAt: editedAt ?? this.editedAt,
-    );
-  }
-}
-
-extension ExpenseCategoryExtension on ExpenseCategory {
-  String get displayName {
-    switch (this) {
-      case ExpenseCategory.restaurant:
-        return 'Restaurant';
-      case ExpenseCategory.transport:
-        return 'Transport';
-      case ExpenseCategory.accommodation:
-        return 'Hébergement';
-      case ExpenseCategory.activities:
-        return 'Activités';
-      case ExpenseCategory.shopping:
-        return 'Shopping';
-      case ExpenseCategory.other:
-        return 'Autre';
-    }
-  }
-
-  IconData get icon {
-    switch (this) {
-      case ExpenseCategory.restaurant:
-        return Icons.restaurant;
-      case ExpenseCategory.transport:
-        return Icons.directions_car;
-      case ExpenseCategory.accommodation:
-        return Icons.hotel;
-      case ExpenseCategory.activities:
-        return Icons.attractions;
-      case ExpenseCategory.shopping:
-        return Icons.shopping_bag;
-      case ExpenseCategory.other:
-        return Icons.more_horiz;
-    }
-  }
-}
-
-extension ExpenseCurrencyExtension on ExpenseCurrency {
-  String get symbol {
-    switch (this) {
-      case ExpenseCurrency.eur:
-        return '€';
-      case ExpenseCurrency.usd:
-        return '\$';
-      case ExpenseCurrency.gbp:
-        return '£';
-      case ExpenseCurrency.jpy:
-        return '¥';
-      case ExpenseCurrency.chf:
-        return 'CHF';
-      case ExpenseCurrency.cad:
-        return 'CAD';
-      case ExpenseCurrency.aud:
-        return 'AUD';
-    }
-  }
-
-  String get code {
-    return name.toUpperCase();
-  }
-}
diff --git a/lib/main.dart b/lib/main.dart
index 13a5030..62ef4e7 100644
--- a/lib/main.dart
+++ b/lib/main.dart
@@ -1,9 +1,13 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:firebase_core/firebase_core.dart';
+import 'package:travel_mate/blocs/balance/balance_bloc.dart';
+import 'package:travel_mate/blocs/expense/expense_bloc.dart';
 import 'package:travel_mate/blocs/message/message_bloc.dart';
+import 'package:travel_mate/services/balance_service.dart';
 import 'package:travel_mate/services/error_service.dart';
-import 'package:flutter_dotenv/flutter_dotenv.dart'; 
+import 'package:flutter_dotenv/flutter_dotenv.dart';
+import 'package:travel_mate/services/expense_service.dart'; 
 import 'blocs/auth/auth_bloc.dart';
 import 'blocs/auth/auth_event.dart';
 import 'blocs/theme/theme_bloc.dart';
@@ -19,6 +23,8 @@ import 'repositories/user_repository.dart';
 import 'repositories/group_repository.dart';
 import 'repositories/message_repository.dart';
 import 'repositories/account_repository.dart';
+import 'repositories/expense_repository.dart';
+import 'repositories/balance_repository.dart';
 import 'pages/login.dart';
 import 'pages/home.dart';
 import 'pages/signup.dart';
@@ -54,6 +60,17 @@ class MyApp extends StatelessWidget {
         RepositoryProvider<MessageRepository>(
           create: (context) => MessageRepository(),
         ),
+        RepositoryProvider<AccountRepository>(
+          create: (context) => AccountRepository(),
+        ),
+        RepositoryProvider<ExpenseRepository>(
+          create: (context) => ExpenseRepository(),
+        ),
+        RepositoryProvider<BalanceRepository>(
+          create: (context) => BalanceRepository(
+            expenseRepository: context.read<ExpenseRepository>(),
+          ),
+        ),
         
       ],
       child: MultiBlocProvider(
@@ -76,7 +93,27 @@ class MyApp extends StatelessWidget {
           BlocProvider(create: (context) => UserBloc()),
           BlocProvider(
             create: (context) => MessageBloc(),
+          ),
+          BlocProvider(
+            create: (context) => AccountBloc(
+              context.read<AccountRepository>(),
             ),
+          ),
+          
+          // Nouveaux blocs
+          BlocProvider<ExpenseBloc>(
+            create: (context) => ExpenseBloc(
+              expenseRepository: context.read<ExpenseRepository>(),
+              expenseService: context.read<ExpenseService>(),
+            ),
+          ),
+          BlocProvider<BalanceBloc>(
+            create: (context) => BalanceBloc(
+              balanceRepository: context.read<BalanceRepository>(),
+              balanceService: context.read<BalanceService>(),
+              expenseRepository: context.read<ExpenseRepository>(),
+            ),
+          ),
           
         ],
         child: BlocBuilder<ThemeBloc, ThemeState>(
diff --git a/lib/data/models/account.dart b/lib/models/account.dart
similarity index 100%
rename from lib/data/models/account.dart
rename to lib/models/account.dart
diff --git a/lib/models/expense.dart b/lib/models/expense.dart
new file mode 100644
index 0000000..a425b0b
--- /dev/null
+++ b/lib/models/expense.dart
@@ -0,0 +1,205 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+import 'package:equatable/equatable.dart';
+import 'package:flutter/material.dart';
+import 'expense_split.dart';
+
+enum ExpenseCurrency {
+  eur('€', 'EUR'),
+  usd('\$', 'USD'),
+  gbp('£', 'GBP');
+
+  const ExpenseCurrency(this.symbol, this.code);
+  final String symbol;
+  final String code;
+}
+
+enum ExpenseCategory {
+  restaurant('Restaurant', Icons.restaurant),
+  transport('Transport', Icons.directions_car),
+  accommodation('Hébergement', Icons.hotel),
+  entertainment('Loisirs', Icons.local_activity),
+  shopping('Shopping', Icons.shopping_bag),
+  other('Autre', Icons.category);
+
+  const ExpenseCategory(this.displayName, this.icon);
+  final String displayName;
+  final IconData icon;
+}
+
+class Expense extends Equatable {
+  final String id;
+  final String groupId;
+  final String description;
+  final double amount;
+  final ExpenseCurrency currency;
+  final double amountInEur; // Montant converti en EUR
+  final ExpenseCategory category;
+  final String paidById;
+  final String paidByName;
+  final DateTime date;
+  final DateTime createdAt;
+  final DateTime? editedAt;
+  final bool isEdited;
+  final bool isArchived;
+  final String? receiptUrl;
+  final List<ExpenseSplit> splits;
+
+  const Expense({
+    required this.id,
+    required this.groupId,
+    required this.description,
+    required this.amount,
+    required this.currency,
+    required this.amountInEur,
+    required this.category,
+    required this.paidById,
+    required this.paidByName,
+    required this.date,
+    required this.createdAt,
+    this.editedAt,
+    this.isEdited = false,
+    this.isArchived = false,
+    this.receiptUrl,
+    required this.splits,
+  });
+
+  factory Expense.fromMap(Map<String, dynamic> map, String id) {
+    return Expense(
+      id: id,
+      groupId: map['groupId'] ?? '',
+      description: map['description'] ?? '',
+      amount: (map['amount'] as num?)?.toDouble() ?? 0.0,
+      currency: ExpenseCurrency.values.firstWhere(
+        (c) => c.code == map['currency'],
+        orElse: () => ExpenseCurrency.eur,
+      ),
+      amountInEur: (map['amountInEur'] as num?)?.toDouble() ?? 0.0,
+      category: ExpenseCategory.values.firstWhere(
+        (c) => c.name == map['category'],
+        orElse: () => ExpenseCategory.other,
+      ),
+      paidById: map['paidById'] ?? '',
+      paidByName: map['paidByName'] ?? '',
+      date: _parseDateTime(map['date']),
+      createdAt: _parseDateTime(map['createdAt']),
+      editedAt: map['editedAt'] != null ? _parseDateTime(map['editedAt']) : null,
+      isEdited: map['isEdited'] ?? false,
+      isArchived: map['isArchived'] ?? false,
+      receiptUrl: map['receiptUrl'],
+      splits: (map['splits'] as List?)
+          ?.map((s) => ExpenseSplit.fromMap(s))
+          .toList() ?? [],
+    );
+  }
+
+  Map<String, dynamic> toMap() {
+    return {
+      'groupId': groupId,
+      'description': description,
+      'amount': amount,
+      'currency': currency.code,
+      'amountInEur': amountInEur,
+      'category': category.name,
+      'paidById': paidById,
+      'paidByName': paidByName,
+      'date': Timestamp.fromDate(date),
+      'createdAt': Timestamp.fromDate(createdAt),
+      'editedAt': editedAt != null ? Timestamp.fromDate(editedAt!) : null,
+      'isEdited': isEdited,
+      'isArchived': isArchived,
+      'receiptUrl': receiptUrl,
+      'splits': splits.map((s) => s.toMap()).toList(),
+    };
+  }
+
+  static DateTime _parseDateTime(dynamic value) {
+    if (value is Timestamp) return value.toDate();
+    if (value is String) return DateTime.parse(value);
+    if (value is DateTime) return value;
+    return DateTime.now();
+  }
+
+  Expense copyWith({
+    String? id,
+    String? groupId,
+    String? description,
+    double? amount,
+    ExpenseCurrency? currency,
+    double? amountInEur,
+    ExpenseCategory? category,
+    String? paidById,
+    String? paidByName,
+    DateTime? date,
+    DateTime? createdAt,
+    DateTime? editedAt,
+    bool? isEdited,
+    bool? isArchived,
+    String? receiptUrl,
+    List<ExpenseSplit>? splits,
+  }) {
+    return Expense(
+      id: id ?? this.id,
+      groupId: groupId ?? this.groupId,
+      description: description ?? this.description,
+      amount: amount ?? this.amount,
+      currency: currency ?? this.currency,
+      amountInEur: amountInEur ?? this.amountInEur,
+      category: category ?? this.category,
+      paidById: paidById ?? this.paidById,
+      paidByName: paidByName ?? this.paidByName,
+      date: date ?? this.date,
+      createdAt: createdAt ?? this.createdAt,
+      editedAt: editedAt ?? this.editedAt,
+      isEdited: isEdited ?? this.isEdited,
+      isArchived: isArchived ?? this.isArchived,
+      receiptUrl: receiptUrl ?? this.receiptUrl,
+      splits: splits ?? this.splits,
+    );
+  }
+
+  Expense copyWithEdit({
+    String? description,
+    double? amount,
+    ExpenseCurrency? currency,
+    double? amountInEur,
+    ExpenseCategory? category,
+    List<ExpenseSplit>? splits,
+    String? receiptUrl,
+  }) {
+    return copyWith(
+      description: description,
+      amount: amount,
+      currency: currency,
+      amountInEur: amountInEur,
+      category: category,
+      splits: splits,
+      receiptUrl: receiptUrl,
+      editedAt: DateTime.now(),
+      isEdited: true,
+    );
+  }
+
+  // Marquer comme archivé
+  Expense copyWithArchived() {
+    return copyWith(
+      isArchived: true,
+    );
+  }
+
+  // Ajouter/mettre à jour l'URL du reçu
+  Expense copyWithReceipt(String receiptUrl) {
+    return copyWith(
+      receiptUrl: receiptUrl,
+    );
+  }
+
+  // Mettre à jour les splits
+  Expense copyWithSplits(List<ExpenseSplit> newSplits) {
+    return copyWith(
+      splits: newSplits,
+    );
+  }
+
+  @override
+  List<Object?> get props => [id];
+}
\ No newline at end of file
diff --git a/lib/models/expense_split.dart b/lib/models/expense_split.dart
new file mode 100644
index 0000000..2f71d38
--- /dev/null
+++ b/lib/models/expense_split.dart
@@ -0,0 +1,58 @@
+import 'package:equatable/equatable.dart';
+
+class ExpenseSplit extends Equatable {
+  final String userId;
+  final String userName;
+  final double amount;
+  final bool isPaid;
+  final DateTime? paidAt;
+
+  const ExpenseSplit({
+    required this.userId,
+    required this.userName,
+    required this.amount,
+    this.isPaid = false,
+    this.paidAt,
+  });
+
+  factory ExpenseSplit.fromMap(Map<String, dynamic> map) {
+    return ExpenseSplit(
+      userId: map['userId'] ?? '',
+      userName: map['userName'] ?? '',
+      amount: (map['amount'] as num?)?.toDouble() ?? 0.0,
+      isPaid: map['isPaid'] ?? false,
+      paidAt: map['paidAt'] != null 
+          ? DateTime.fromMillisecondsSinceEpoch(map['paidAt'])
+          : null,
+    );
+  }
+
+  Map<String, dynamic> toMap() {
+    return {
+      'userId': userId,
+      'userName': userName,
+      'amount': amount,
+      'isPaid': isPaid,
+      'paidAt': paidAt?.millisecondsSinceEpoch,
+    };
+  }
+
+  ExpenseSplit copyWith({
+    String? userId,
+    String? userName,
+    double? amount,
+    bool? isPaid,
+    DateTime? paidAt,
+  }) {
+    return ExpenseSplit(
+      userId: userId ?? this.userId,
+      userName: userName ?? this.userName,
+      amount: amount ?? this.amount,
+      isPaid: isPaid ?? this.isPaid,
+      paidAt: paidAt ?? this.paidAt,
+    );
+  }
+
+  @override
+  List<Object?> get props => [userId, userName, amount, isPaid];
+}
\ No newline at end of file
diff --git a/lib/data/models/group.dart b/lib/models/group.dart
similarity index 100%
rename from lib/data/models/group.dart
rename to lib/models/group.dart
diff --git a/lib/models/group_balance.dart b/lib/models/group_balance.dart
new file mode 100644
index 0000000..1d121ec
--- /dev/null
+++ b/lib/models/group_balance.dart
@@ -0,0 +1,93 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+import 'package:equatable/equatable.dart';
+import 'user_balance.dart';
+import 'settlement.dart';
+
+class GroupBalance extends Equatable {
+  final String groupId;
+  final List<UserBalance> userBalances;
+  final List<Settlement> settlements;
+  final double totalExpenses;
+  final DateTime calculatedAt;
+
+  const GroupBalance({
+    required this.groupId,
+    required this.userBalances,
+    required this.settlements,
+    required this.totalExpenses,
+    required this.calculatedAt,
+  });
+
+  // Constructeur factory pour créer depuis une Map
+  factory GroupBalance.fromMap(Map<String, dynamic> map) {
+    return GroupBalance(
+      groupId: map['groupId'] ?? '',
+      userBalances: (map['userBalances'] as List?)
+          ?.map((userBalance) => UserBalance.fromMap(userBalance as Map<String, dynamic>))
+          .toList() ?? [],
+      settlements: (map['settlements'] as List?)
+          ?.map((settlement) => Settlement.fromMap(settlement as Map<String, dynamic>))
+          .toList() ?? [],
+      totalExpenses: (map['totalExpenses'] as num?)?.toDouble() ?? 0.0,
+      calculatedAt: _parseDateTime(map['calculatedAt']),
+    );
+  }
+
+  // Convertir en Map pour Firestore
+  Map<String, dynamic> toMap() {
+    return {
+      'groupId': groupId,
+      'userBalances': userBalances.map((userBalance) => userBalance.toMap()).toList(),
+      'settlements': settlements.map((settlement) => settlement.toMap()).toList(),
+      'totalExpenses': totalExpenses,
+      'calculatedAt': Timestamp.fromDate(calculatedAt),
+    };
+  }
+
+  // Méthode copyWith pour créer une copie modifiée
+  GroupBalance copyWith({
+    String? groupId,
+    List<UserBalance>? userBalances,
+    List<Settlement>? settlements,
+    double? totalExpenses,
+    DateTime? calculatedAt,
+  }) {
+    return GroupBalance(
+      groupId: groupId ?? this.groupId,
+      userBalances: userBalances ?? this.userBalances,
+      settlements: settlements ?? this.settlements,
+      totalExpenses: totalExpenses ?? this.totalExpenses,
+      calculatedAt: calculatedAt ?? this.calculatedAt,
+    );
+  }
+
+  // Helper pour parser les dates de différents formats
+  static DateTime _parseDateTime(dynamic value) {
+    if (value is Timestamp) return value.toDate();
+    if (value is String) return DateTime.parse(value);
+    if (value is DateTime) return value;
+    if (value is int) return DateTime.fromMillisecondsSinceEpoch(value);
+    return DateTime.now();
+  }
+
+  // Méthodes utilitaires pour la logique métier
+  bool get hasUnbalancedUsers => userBalances.any((balance) => !balance.isBalanced);
+  
+  bool get hasSettlements => settlements.isNotEmpty;
+  
+  double get totalSettlementAmount => settlements.fold(0.0, (sum, settlement) => sum + settlement.amount);
+  
+  List<UserBalance> get creditors => userBalances.where((b) => b.shouldReceive).toList();
+  
+  List<UserBalance> get debtors => userBalances.where((b) => b.shouldPay).toList();
+  
+  int get participantCount => userBalances.length;
+
+  @override
+  List<Object?> get props => [groupId, calculatedAt];
+
+  @override
+  String toString() {
+    return 'GroupBalance(groupId: $groupId, totalExpenses: $totalExpenses, participantCount: $participantCount, calculatedAt: $calculatedAt)';
+  }
+}
\ No newline at end of file
diff --git a/lib/data/models/group_member.dart b/lib/models/group_member.dart
similarity index 100%
rename from lib/data/models/group_member.dart
rename to lib/models/group_member.dart
diff --git a/lib/models/group_statistics.dart b/lib/models/group_statistics.dart
new file mode 100644
index 0000000..fe83430
--- /dev/null
+++ b/lib/models/group_statistics.dart
@@ -0,0 +1,25 @@
+class GroupStatistics {
+  final double totalExpenses;
+  final int expenseCount;
+  final double averageExpense;
+  final String topCategory;
+  final Map<String, double> categoryBreakdown;
+
+  const GroupStatistics({
+    required this.totalExpenses,
+    required this.expenseCount,
+    required this.averageExpense,
+    required this.topCategory,
+    required this.categoryBreakdown,
+  });
+
+  factory GroupStatistics.empty() {
+    return const GroupStatistics(
+      totalExpenses: 0.0,
+      expenseCount: 0,
+      averageExpense: 0.0,
+      topCategory: '',
+      categoryBreakdown: {},
+    );
+  }
+}
\ No newline at end of file
diff --git a/lib/data/models/message.dart b/lib/models/message.dart
similarity index 100%
rename from lib/data/models/message.dart
rename to lib/models/message.dart
diff --git a/lib/models/settlement.dart b/lib/models/settlement.dart
new file mode 100644
index 0000000..ec9de30
--- /dev/null
+++ b/lib/models/settlement.dart
@@ -0,0 +1,130 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+import 'package:equatable/equatable.dart';
+
+class Settlement extends Equatable {
+  final String fromUserId;
+  final String fromUserName;
+  final String toUserId;
+  final String toUserName;
+  final double amount;
+  final bool isCompleted;
+  final DateTime? completedAt;
+
+  const Settlement({
+    required this.fromUserId,
+    required this.fromUserName,
+    required this.toUserId,
+    required this.toUserName,
+    required this.amount,
+    this.isCompleted = false,
+    this.completedAt,
+  });
+
+  // Constructeur factory pour créer depuis une Map
+  factory Settlement.fromMap(Map<String, dynamic> map) {
+    return Settlement(
+      fromUserId: map['fromUserId'] ?? '',
+      fromUserName: map['fromUserName'] ?? '',
+      toUserId: map['toUserId'] ?? '',
+      toUserName: map['toUserName'] ?? '',
+      amount: (map['amount'] as num?)?.toDouble() ?? 0.0,
+      isCompleted: map['isCompleted'] ?? false,
+      completedAt: map['completedAt'] != null 
+          ? _parseDateTime(map['completedAt'])
+          : null,
+    );
+  }
+
+  // Convertir en Map pour la sérialisation
+  Map<String, dynamic> toMap() {
+    return {
+      'fromUserId': fromUserId,
+      'fromUserName': fromUserName,
+      'toUserId': toUserId,
+      'toUserName': toUserName,
+      'amount': amount,
+      'isCompleted': isCompleted,
+      'completedAt': completedAt != null 
+          ? Timestamp.fromDate(completedAt!)
+          : null,
+    };
+  }
+
+  // Méthode copyWith étendue pour créer une copie modifiée
+  Settlement copyWith({
+    String? fromUserId,
+    String? fromUserName,
+    String? toUserId,
+    String? toUserName,
+    double? amount,
+    bool? isCompleted,
+    DateTime? completedAt,
+  }) {
+    return Settlement(
+      fromUserId: fromUserId ?? this.fromUserId,
+      fromUserName: fromUserName ?? this.fromUserName,
+      toUserId: toUserId ?? this.toUserId,
+      toUserName: toUserName ?? this.toUserName,
+      amount: amount ?? this.amount,
+      isCompleted: isCompleted ?? this.isCompleted,
+      completedAt: completedAt ?? this.completedAt,
+    );
+  }
+
+  // Constructeur factory pour marquer comme complété
+  factory Settlement.completed(Settlement settlement) {
+    return settlement.copyWith(
+      isCompleted: true,
+      completedAt: DateTime.now(),
+    );
+  }
+
+  // Helper pour parser les dates de différents formats
+  static DateTime _parseDateTime(dynamic value) {
+    if (value is Timestamp) return value.toDate();
+    if (value is String) return DateTime.parse(value);
+    if (value is DateTime) return value;
+    if (value is int) return DateTime.fromMillisecondsSinceEpoch(value);
+    return DateTime.now();
+  }
+
+  // Getters utilitaires pour la logique métier
+  bool get isPending => !isCompleted;
+  
+  String get formattedAmount => '${amount.toStringAsFixed(2)} €';
+  
+  String get description => '$fromUserName doit ${formattedAmount} à $toUserName';
+  
+  String get shortDescription => '$fromUserName → $toUserName';
+  
+  String get status => isCompleted ? 'Payé' : 'En attente';
+  
+  // Durée depuis la completion (si applicable)
+  Duration? get timeSinceCompletion {
+    if (completedAt == null) return null;
+    return DateTime.now().difference(completedAt!);
+  }
+  
+  // Formatage de la date de completion
+  String get formattedCompletedAt {
+    if (completedAt == null) return 'Non payé';
+    return 'Payé le ${completedAt!.day}/${completedAt!.month}/${completedAt!.year}';
+  }
+
+  // Méthodes de validation
+  bool get isValid => 
+      fromUserId.isNotEmpty && 
+      toUserId.isNotEmpty && 
+      fromUserId != toUserId && 
+      amount > 0;
+
+  bool get isSelfSettlement => fromUserId == toUserId;
+
+  @override
+  List<Object?> get props => [fromUserId, toUserId, amount, isCompleted];
+
+  @override
+  String toString() {
+    return 'Settlement(${shortDescription}: ${formattedAmount}, status: $status)';
+  }
+}
\ No newline at end of file
diff --git a/lib/data/models/trip.dart b/lib/models/trip.dart
similarity index 100%
rename from lib/data/models/trip.dart
rename to lib/models/trip.dart
diff --git a/lib/data/models/user.dart b/lib/models/user.dart
similarity index 100%
rename from lib/data/models/user.dart
rename to lib/models/user.dart
diff --git a/lib/models/user_balance.dart b/lib/models/user_balance.dart
new file mode 100644
index 0000000..4a23260
--- /dev/null
+++ b/lib/models/user_balance.dart
@@ -0,0 +1,98 @@
+import 'package:equatable/equatable.dart';
+
+class UserBalance extends Equatable {
+  final String userId;
+  final String userName;
+  final double totalPaid;     // Total payé par cet utilisateur
+  final double totalOwed;     // Total dû par cet utilisateur
+  final double balance;       // Différence (positif = à recevoir, négatif = à payer)
+
+  const UserBalance({
+    required this.userId,
+    required this.userName,
+    required this.totalPaid,
+    required this.totalOwed,
+    required this.balance,
+  });
+
+  // Constructeur factory pour créer depuis une Map
+  factory UserBalance.fromMap(Map<String, dynamic> map) {
+    return UserBalance(
+      userId: map['userId'] ?? '',
+      userName: map['userName'] ?? '',
+      totalPaid: (map['totalPaid'] as num?)?.toDouble() ?? 0.0,
+      totalOwed: (map['totalOwed'] as num?)?.toDouble() ?? 0.0,
+      balance: (map['balance'] as num?)?.toDouble() ?? 0.0,
+    );
+  }
+
+  // Convertir en Map pour la sérialisation
+  Map<String, dynamic> toMap() {
+    return {
+      'userId': userId,
+      'userName': userName,
+      'totalPaid': totalPaid,
+      'totalOwed': totalOwed,
+      'balance': balance,
+    };
+  }
+
+  // Méthode copyWith pour créer une copie modifiée
+  UserBalance copyWith({
+    String? userId,
+    String? userName,
+    double? totalPaid,
+    double? totalOwed,
+    double? balance,
+  }) {
+    return UserBalance(
+      userId: userId ?? this.userId,
+      userName: userName ?? this.userName,
+      totalPaid: totalPaid ?? this.totalPaid,
+      totalOwed: totalOwed ?? this.totalOwed,
+      balance: balance ?? this.balance,
+    );
+  }
+
+  // Constructeur factory pour recalculer automatiquement la balance
+  factory UserBalance.calculated({
+    required String userId,
+    required String userName,
+    required double totalPaid,
+    required double totalOwed,
+  }) {
+    return UserBalance(
+      userId: userId,
+      userName: userName,
+      totalPaid: totalPaid,
+      totalOwed: totalOwed,
+      balance: totalPaid - totalOwed,
+    );
+  }
+
+  // Getters pour la logique métier
+  bool get shouldReceive => balance > 0;
+  bool get shouldPay => balance < 0;
+  bool get isBalanced => balance.abs() < 0.01; // Tolérance pour les arrondis
+
+  // Montants absolus pour l'affichage
+  double get absoluteBalance => balance.abs();
+  String get balanceStatus {
+    if (isBalanced) return 'Équilibré';
+    if (shouldReceive) return 'À recevoir';
+    return 'À payer';
+  }
+
+  // Formatage pour l'affichage
+  String get formattedBalance => '${absoluteBalance.toStringAsFixed(2)} €';
+  String get formattedTotalPaid => '${totalPaid.toStringAsFixed(2)} €';
+  String get formattedTotalOwed => '${totalOwed.toStringAsFixed(2)} €';
+
+  @override
+  List<Object?> get props => [userId, userName, balance];
+
+  @override
+  String toString() {
+    return 'UserBalance(userId: $userId, userName: $userName, balance: ${balance.toStringAsFixed(2)}€)';
+  }
+}
\ No newline at end of file
diff --git a/lib/pages/home.dart b/lib/pages/home.dart
index 99d9746..3535370 100644
--- a/lib/pages/home.dart
+++ b/lib/pages/home.dart
@@ -58,7 +58,7 @@ class _HomePageState extends State<HomePage> {
         page = const GroupContent();
         break;
       case 4:
-        page = const CountContent();
+        page = const AccountContent();
         break;
       default:
         page = const HomeContent();
diff --git a/lib/repositories/account_repository.dart b/lib/repositories/account_repository.dart
index ee9b29f..c7f4c74 100644
--- a/lib/repositories/account_repository.dart
+++ b/lib/repositories/account_repository.dart
@@ -1,7 +1,7 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:travel_mate/services/error_service.dart';
-import '../data/models/group_member.dart';
-import '../data/models/account.dart';
+import '../models/group_member.dart';
+import '../models/account.dart';
 
 class AccountRepository {
   final FirebaseFirestore _firestore = FirebaseFirestore.instance;
diff --git a/lib/repositories/auth_repository.dart b/lib/repositories/auth_repository.dart
index fe27641..bab8ccd 100644
--- a/lib/repositories/auth_repository.dart
+++ b/lib/repositories/auth_repository.dart
@@ -1,6 +1,6 @@
 import 'package:firebase_auth/firebase_auth.dart' as firebase_auth;
 import 'package:cloud_firestore/cloud_firestore.dart';
-import '../data/models/user.dart';
+import '../models/user.dart';
 import '../services/auth_service.dart';
 
 class AuthRepository {
diff --git a/lib/repositories/balance_repository.dart b/lib/repositories/balance_repository.dart
new file mode 100644
index 0000000..db8e941
--- /dev/null
+++ b/lib/repositories/balance_repository.dart
@@ -0,0 +1,146 @@
+import '../models/group_balance.dart';
+import '../models/expense.dart';
+import '../services/error_service.dart';
+import 'expense_repository.dart';
+import '../models/user_balance.dart';
+import '../models/settlement.dart';
+
+class BalanceRepository {
+  final ExpenseRepository _expenseRepository;
+  final ErrorService _errorService;
+
+  BalanceRepository({
+    required ExpenseRepository expenseRepository,
+    ErrorService? errorService,
+  }) : _expenseRepository = expenseRepository,
+       _errorService = errorService ?? ErrorService();
+
+  // Calculer la balance d'un groupe
+  Future<GroupBalance> calculateGroupBalance(String groupId) async {
+    try {
+      // Pour l'instant, on utilise une liste statique des dépenses
+      // En production, vous récupéreriez depuis le stream
+      final expenses = await _expenseRepository
+          .getExpensesStream(groupId)
+          .first;
+
+      final userBalances = _calculateUserBalances(expenses);
+      final settlements = _calculateOptimalSettlements(userBalances);
+      final totalExpenses = expenses
+          .where((e) => !e.isArchived)
+          .fold(0.0, (sum, e) => sum + e.amountInEur);
+
+      return GroupBalance(
+        groupId: groupId,
+        userBalances: userBalances,
+        settlements: settlements,
+        totalExpenses: totalExpenses,
+        calculatedAt: DateTime.now(),
+      );
+    } catch (e) {
+      _errorService.logError('BalanceRepository', 'Erreur calcul balance: $e');
+      rethrow;
+    }
+  }
+
+  // Calculer les balances individuelles
+  List<UserBalance> _calculateUserBalances(List<Expense> expenses) {
+    final Map<String, Map<String, dynamic>> userBalanceMap = {};
+
+    // Initialiser les utilisateurs
+    for (final expense in expenses) {
+      if (expense.isArchived) continue;
+
+      // Ajouter le payeur
+      userBalanceMap.putIfAbsent(expense.paidById, () => {
+        'name': expense.paidByName,
+        'paid': 0.0,
+        'owed': 0.0,
+      });
+
+      // Ajouter les participants
+      for (final split in expense.splits) {
+        userBalanceMap.putIfAbsent(split.userId, () => {
+          'name': split.userName,
+          'paid': 0.0,
+          'owed': 0.0,
+        });
+      }
+    }
+
+    // Calculer les montants
+    for (final expense in expenses) {
+      if (expense.isArchived) continue;
+
+      // Ajouter au montant payé
+      userBalanceMap[expense.paidById]!['paid'] += expense.amountInEur;
+
+      // Ajouter aux montants dus
+      for (final split in expense.splits) {
+        userBalanceMap[split.userId]!['owed'] += split.amount;
+      }
+    }
+
+    // Convertir en liste de UserBalance
+    return userBalanceMap.entries.map((entry) {
+      final userId = entry.key;
+      final data = entry.value;
+      final paid = data['paid'] as double;
+      final owed = data['owed'] as double;
+      
+      return UserBalance(
+        userId: userId,
+        userName: data['name'] as String,
+        totalPaid: paid,
+        totalOwed: owed,
+        balance: paid - owed,
+      );
+    }).toList();
+  }
+
+  // Algorithme d'optimisation des règlements
+  List<Settlement> _calculateOptimalSettlements(List<UserBalance> balances) {
+    final settlements = <Settlement>[];
+    
+    // Séparer les créditeurs et débiteurs
+    final creditors = balances.where((b) => b.shouldReceive).toList();
+    final debtors = balances.where((b) => b.shouldPay).toList();
+
+    // Trier par montant (plus gros montants en premier)
+    creditors.sort((a, b) => b.balance.compareTo(a.balance));
+    debtors.sort((a, b) => a.balance.compareTo(b.balance));
+
+    // Créer des copies mutables des montants
+    final creditorsRemaining = Map.fromEntries(
+      creditors.map((c) => MapEntry(c.userId, c.balance))
+    );
+    final debtorsRemaining = Map.fromEntries(
+      debtors.map((d) => MapEntry(d.userId, -d.balance))
+    );
+
+    // Algorithme glouton pour minimiser le nombre de transactions
+    for (final creditor in creditors) {
+      for (final debtor in debtors) {
+        final creditAmount = creditorsRemaining[creditor.userId] ?? 0;
+        final debtAmount = debtorsRemaining[debtor.userId] ?? 0;
+
+        if (creditAmount <= 0.01 || debtAmount <= 0.01) continue;
+
+        final settlementAmount = [creditAmount, debtAmount].reduce((a, b) => a < b ? a : b);
+
+        settlements.add(Settlement(
+          fromUserId: debtor.userId,
+          fromUserName: debtor.userName,
+          toUserId: creditor.userId,
+          toUserName: creditor.userName,
+          amount: settlementAmount,
+        ));
+
+        creditorsRemaining[creditor.userId] = creditAmount - settlementAmount;
+        debtorsRemaining[debtor.userId] = debtAmount - settlementAmount;
+      }
+    }
+
+    return settlements;
+  }
+}
\ No newline at end of file
diff --git a/lib/repositories/expense_repository.dart b/lib/repositories/expense_repository.dart
new file mode 100644
index 0000000..d148246
--- /dev/null
+++ b/lib/repositories/expense_repository.dart
@@ -0,0 +1,113 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+import '../models/expense.dart';
+import '../services/error_service.dart';
+
+class ExpenseRepository {
+  final FirebaseFirestore _firestore;
+  final ErrorService _errorService;
+
+  ExpenseRepository({
+    FirebaseFirestore? firestore,
+    ErrorService? errorService,
+  }) : _firestore = firestore ?? FirebaseFirestore.instance,
+       _errorService = errorService ?? ErrorService();
+
+  CollectionReference get _expensesCollection => _firestore.collection('expenses');
+
+  // Stream des dépenses d'un groupe
+  Stream<List<Expense>> getExpensesStream(String groupId) {
+    return _expensesCollection
+        .where('groupId', isEqualTo: groupId)
+        .where('isArchived', isEqualTo: false)
+        .orderBy('createdAt', descending: true)
+        .snapshots()
+        .map((snapshot) {
+      return snapshot.docs
+          .map((doc) => Expense.fromMap(doc.data() as Map<String, dynamic>, doc.id))
+          .toList();
+    }).handleError((error) {
+      _errorService.logError('ExpenseRepository', 'Erreur stream expenses: $error');
+      return <Expense>[];
+    });
+  }
+
+  // Créer une dépense
+  Future<String> createExpense(Expense expense) async {
+    try {
+      final docRef = await _expensesCollection.add(expense.toMap());
+      return docRef.id;
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur création expense: $e');
+      rethrow;
+    }
+  }
+
+  // Mettre à jour une dépense
+  Future<void> updateExpense(Expense expense) async {
+    try {
+      final updateData = expense.toMap();
+      updateData['editedAt'] = FieldValue.serverTimestamp();
+      updateData['isEdited'] = true;
+      
+      await _expensesCollection.doc(expense.id).update(updateData);
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur update expense: $e');
+      rethrow;
+    }
+  }
+
+  // Supprimer une dépense
+  Future<void> deleteExpense(String expenseId) async {
+    try {
+      await _expensesCollection.doc(expenseId).delete();
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur delete expense: $e');
+      rethrow;
+    }
+  }
+
+  // Marquer un split comme payé
+  Future<void> markSplitAsPaid(String expenseId, String userId) async {
+    try {
+      await _firestore.runTransaction((transaction) async {
+        final expenseDoc = await transaction.get(_expensesCollection.doc(expenseId));
+        
+        if (!expenseDoc.exists) {
+          throw Exception('Dépense non trouvée');
+        }
+
+        final expense = Expense.fromMap(
+          expenseDoc.data() as Map<String, dynamic>, 
+          expenseDoc.id
+        );
+
+        final updatedSplits = expense.splits.map((split) {
+          if (split.userId == userId) {
+            return split.copyWith(isPaid: true, paidAt: DateTime.now());
+          }
+          return split;
+        }).toList();
+
+        transaction.update(expenseDoc.reference, {
+          'splits': updatedSplits.map((s) => s.toMap()).toList(),
+        });
+      });
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur mark split paid: $e');
+      rethrow;
+    }
+  }
+
+  // Archiver une dépense
+  Future<void> archiveExpense(String expenseId) async {
+    try {
+      await _expensesCollection.doc(expenseId).update({
+        'isArchived': true,
+        'archivedAt': FieldValue.serverTimestamp(),
+      });
+    } catch (e) {
+      _errorService.logError('ExpenseRepository', 'Erreur archive expense: $e');
+      rethrow;
+    }
+  }
+}
\ No newline at end of file
diff --git a/lib/repositories/group_repository.dart b/lib/repositories/group_repository.dart
index 3698218..bd02b6f 100644
--- a/lib/repositories/group_repository.dart
+++ b/lib/repositories/group_repository.dart
@@ -1,7 +1,7 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:travel_mate/services/error_service.dart';
-import '../data/models/group.dart';
-import '../data/models/group_member.dart';
+import '../models/group.dart';
+import '../models/group_member.dart';
 
 class GroupRepository {
   final FirebaseFirestore _firestore = FirebaseFirestore.instance;
diff --git a/lib/repositories/message_repository.dart b/lib/repositories/message_repository.dart
index 832640e..a35dc83 100644
--- a/lib/repositories/message_repository.dart
+++ b/lib/repositories/message_repository.dart
@@ -1,5 +1,5 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
-import '../data/models/message.dart';
+import '../models/message.dart';
 
 class MessageRepository {
   final FirebaseFirestore _firestore;
diff --git a/lib/repositories/trip_repository.dart b/lib/repositories/trip_repository.dart
index b208dcf..38a4767 100644
--- a/lib/repositories/trip_repository.dart
+++ b/lib/repositories/trip_repository.dart
@@ -1,5 +1,5 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
-import '../data/models/trip.dart';
+import '../models/trip.dart';
 
 class TripRepository {
   final FirebaseFirestore _firestore = FirebaseFirestore.instance;
diff --git a/lib/repositories/user_repository.dart b/lib/repositories/user_repository.dart
index f1b591f..8caaab8 100644
--- a/lib/repositories/user_repository.dart
+++ b/lib/repositories/user_repository.dart
@@ -1,5 +1,5 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
-import '../data/models/user.dart';
+import '../models/user.dart';
 import '../services/auth_service.dart';
 
 class UserRepository {
diff --git a/lib/services/account_service.dart b/lib/services/account_service.dart
index e42265a..3b9eed4 100644
--- a/lib/services/account_service.dart
+++ b/lib/services/account_service.dart
@@ -1,6 +1,6 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:travel_mate/services/error_service.dart';
-import '../data/models/account.dart';
+import '../models/account.dart';
 
 class AccountService {
   final _errorService = ErrorService();
diff --git a/lib/services/balance_service.dart b/lib/services/balance_service.dart
new file mode 100644
index 0000000..712a024
--- /dev/null
+++ b/lib/services/balance_service.dart
@@ -0,0 +1,267 @@
+import '../models/group_balance.dart';
+import '../models/expense.dart';
+import '../models/group_statistics.dart';
+import '../models/user_balance.dart';
+import '../models/settlement.dart';
+import '../repositories/balance_repository.dart';
+import '../repositories/expense_repository.dart';
+import 'error_service.dart';
+
+class BalanceService {
+  final BalanceRepository _balanceRepository;
+  final ExpenseRepository _expenseRepository;
+  final ErrorService _errorService;
+
+  BalanceService({
+    required BalanceRepository balanceRepository,
+    required ExpenseRepository expenseRepository,
+    ErrorService? errorService,
+  }) : _balanceRepository = balanceRepository,
+       _expenseRepository = expenseRepository,
+       _errorService = errorService ?? ErrorService();
+
+  /// Calculer la balance complète d'un groupe
+  Future<GroupBalance> calculateGroupBalance(String groupId) async {
+    try {
+      return await _balanceRepository.calculateGroupBalance(groupId);
+    } catch (e) {
+      _errorService.logError('BalanceService', 'Erreur calcul balance groupe: $e');
+      rethrow;
+    }
+  }
+
+  /// Stream de la balance en temps réel
+  Stream<GroupBalance> getGroupBalanceStream(String groupId) {
+    return _expenseRepository.getExpensesStream(groupId).asyncMap((expenses) async {
+      try {
+        final userBalances = calculateUserBalances(expenses);
+        final settlements = optimizeSettlements(userBalances);
+        final totalExpenses = expenses
+            .where((e) => !e.isArchived)
+            .fold(0.0, (sum, e) => sum + e.amountInEur);
+
+        return GroupBalance(
+          groupId: groupId,
+          userBalances: userBalances,
+          settlements: settlements,
+          totalExpenses: totalExpenses,
+          calculatedAt: DateTime.now(),
+        );
+      } catch (e) {
+        _errorService.logError('BalanceService', 'Erreur stream balance: $e');
+        rethrow;
+      }
+    });
+  }
+
+  /// Calculer les balances individuelles (logique métier)
+  List<UserBalance> calculateUserBalances(List<Expense> expenses) {
+    final Map<String, _UserBalanceCalculator> calculators = {};
+
+    // Initialiser les calculateurs pour chaque utilisateur
+    for (final expense in expenses) {
+      if (expense.isArchived) continue;
+
+      // Ajouter le payeur
+      calculators.putIfAbsent(
+        expense.paidById,
+        () => _UserBalanceCalculator(expense.paidById, expense.paidByName),
+      );
+
+      // Ajouter les participants
+      for (final split in expense.splits) {
+        calculators.putIfAbsent(
+          split.userId,
+          () => _UserBalanceCalculator(split.userId, split.userName),
+        );
+      }
+    }
+
+    // Calculer les montants
+    for (final expense in expenses) {
+      if (expense.isArchived) continue;
+
+      // Ajouter au montant payé
+      calculators[expense.paidById]!.addPaid(expense.amountInEur);
+
+      // Ajouter aux montants dus
+      for (final split in expense.splits) {
+        calculators[split.userId]!.addOwed(split.amount);
+      }
+    }
+
+    // Convertir en UserBalance
+    return calculators.values.map((calc) => calc.toUserBalance()).toList();
+  }
+
+  /// Optimiser les règlements (algorithme avancé)
+  List<Settlement> optimizeSettlements(List<UserBalance> balances) {
+    final settlements = <Settlement>[];
+    
+    // Filtrer les utilisateurs avec une balance significative (> 0.01€)
+    final creditors = balances
+        .where((b) => b.shouldReceive && b.balance > 0.01)
+        .toList();
+    final debtors = balances
+        .where((b) => b.shouldPay && b.balance < -0.01)
+        .toList();
+
+    if (creditors.isEmpty || debtors.isEmpty) {
+      return settlements;
+    }
+
+    // Trier par montant absolu décroissant pour optimiser
+    creditors.sort((a, b) => b.balance.compareTo(a.balance));
+    debtors.sort((a, b) => a.balance.compareTo(b.balance));
+
+    // Utiliser des copies mutables pour les calculs
+    final creditorsRemaining = Map<String, double>.fromEntries(
+      creditors.map((c) => MapEntry(c.userId, c.balance))
+    );
+    final debtorsRemaining = Map<String, double>.fromEntries(
+      debtors.map((d) => MapEntry(d.userId, -d.balance))
+    );
+
+    // Algorithme glouton optimisé
+    for (final creditor in creditors) {
+      final creditRemaining = creditorsRemaining[creditor.userId] ?? 0;
+      if (creditRemaining <= 0.01) continue;
+
+      for (final debtor in debtors) {
+        final debtRemaining = debtorsRemaining[debtor.userId] ?? 0;
+        if (debtRemaining <= 0.01) continue;
+
+        final settlementAmount = _calculateOptimalSettlementAmount(
+          creditRemaining,
+          debtRemaining,
+        );
+
+        if (settlementAmount > 0.01) {
+          settlements.add(Settlement(
+            fromUserId: debtor.userId,
+            fromUserName: debtor.userName,
+            toUserId: creditor.userId,
+            toUserName: creditor.userName,
+            amount: settlementAmount,
+          ));
+
+          // Mettre à jour les montants restants
+          creditorsRemaining[creditor.userId] = creditRemaining - settlementAmount;
+          debtorsRemaining[debtor.userId] = debtRemaining - settlementAmount;
+        }
+      }
+    }
+
+    return _validateSettlements(settlements);
+  }
+
+  /// Calculer le montant optimal pour un règlement
+  double _calculateOptimalSettlementAmount(double creditAmount, double debtAmount) {
+    final amount = [creditAmount, debtAmount].reduce((a, b) => a < b ? a : b);
+    // Arrondir à 2 décimales
+    return (amount * 100).round() / 100;
+  }
+
+  /// Valider les règlements calculés
+  List<Settlement> _validateSettlements(List<Settlement> settlements) {
+    // Supprimer les règlements trop petits
+    final validSettlements = settlements
+        .where((s) => s.amount > 0.01)
+        .toList();
+
+    // Log pour debug en cas de problème
+    final totalSettlements = validSettlements.fold(0.0, (sum, s) => sum + s.amount);
+    _errorService.logInfo('BalanceService', 
+        'Règlements calculés: ${validSettlements.length}, Total: ${totalSettlements.toStringAsFixed(2)}€');
+
+    return validSettlements;
+  }
+
+  /// Calculer la dette entre deux utilisateurs spécifiques
+  double calculateDebtBetweenUsers(String groupId, String userId1, String userId2) {
+    // Cette méthode pourrait être utile pour des fonctionnalités avancées
+    // comme "Combien me doit X ?" ou "Combien je dois à Y ?"
+    return 0.0; // TODO: Implémenter si nécessaire
+  }
+
+  /// Analyser les tendances de dépenses par catégorie
+  Map<String, double> analyzeCategorySpending(List<Expense> expenses) {
+    final categoryTotals = <String, double>{};
+    
+    for (final expense in expenses) {
+      if (expense.isArchived) continue;
+      
+      final categoryName = expense.category.displayName;
+      categoryTotals[categoryName] = (categoryTotals[categoryName] ?? 0) + expense.amountInEur;
+    }
+    
+    return categoryTotals;
+  }
+
+  /// Calculer les statistiques du groupe
+  GroupStatistics calculateGroupStatistics(List<Expense> expenses) {
+    if (expenses.isEmpty) {
+      return GroupStatistics.empty();
+    }
+
+    final nonArchivedExpenses = expenses.where((e) => !e.isArchived).toList();
+    final totalAmount = nonArchivedExpenses.fold(0.0, (sum, e) => sum + e.amountInEur);
+    final averageAmount = totalAmount / nonArchivedExpenses.length;
+    
+    final categorySpending = analyzeCategorySpending(nonArchivedExpenses);
+    final topCategory = categorySpending.entries
+        .reduce((a, b) => a.value > b.value ? a : b)
+        .key;
+
+    return GroupStatistics(
+      totalExpenses: totalAmount,
+      expenseCount: nonArchivedExpenses.length,
+      averageExpense: averageAmount,
+      topCategory: topCategory,
+      categoryBreakdown: categorySpending,
+    );
+  }
+
+  Future<void> markSettlementAsCompleted({
+    required String groupId,
+    required String fromUserId,
+    required String toUserId,
+    required double amount,
+  }) async {
+    try {
+      // Ici vous pourriez enregistrer le règlement en base
+      // ou créer une transaction de règlement
+      
+      // Pour l'instant, on pourrait juste recalculer
+      await Future.delayed(const Duration(milliseconds: 100));
+      
+      _errorService.logSuccess('BalanceService', 'Règlement marqué comme effectué');
+    } catch (e) {
+      _errorService.logError('BalanceService', 'Erreur mark settlement: $e');
+      rethrow;
+    }
+  }
+}
+
+/// Classe helper pour calculer les balances
+class _UserBalanceCalculator {
+  final String userId;
+  final String userName;
+  double _totalPaid = 0.0;
+  double _totalOwed = 0.0;
+
+  _UserBalanceCalculator(this.userId, this.userName);
+
+  void addPaid(double amount) => _totalPaid += amount;
+  void addOwed(double amount) => _totalOwed += amount;
+
+  UserBalance toUserBalance() {
+    return UserBalance(
+      userId: userId,
+      userName: userName,
+      totalPaid: _totalPaid,
+      totalOwed: _totalOwed,
+      balance: _totalPaid - _totalOwed,
+    );
+  }
+}
\ No newline at end of file
diff --git a/lib/services/expense_service.dart b/lib/services/expense_service.dart
new file mode 100644
index 0000000..c7e1fe2
--- /dev/null
+++ b/lib/services/expense_service.dart
@@ -0,0 +1,91 @@
+import 'dart:io';
+import '../models/expense.dart';
+import '../repositories/expense_repository.dart';
+import 'error_service.dart';
+import 'storage_service.dart'; // Pour upload des reçus
+
+class ExpenseService {
+  final ExpenseRepository _expenseRepository;
+  final ErrorService _errorService;
+  final StorageService _storageService;
+
+  ExpenseService({
+    required ExpenseRepository expenseRepository,
+    ErrorService? errorService,
+    StorageService? storageService,
+  }) : _expenseRepository = expenseRepository,
+       _errorService = errorService ?? ErrorService(),
+       _storageService = storageService ?? StorageService();
+
+  // Création avec validation et upload d'image
+  Future<String> createExpenseWithValidation(Expense expense, File? receiptImage) async {
+    try {
+      // Validation métier
+      _validateExpenseData(expense);
+      
+      // Upload du reçu si présent
+      String? receiptUrl;
+      if (receiptImage != null) {
+        receiptUrl = await _storageService.uploadReceiptImage(
+          expense.groupId,
+          receiptImage,
+        );
+      }
+      
+      // Créer l'expense avec l'URL du reçu
+      final expenseWithReceipt = expense.copyWith(receiptUrl: receiptUrl);
+      
+      return await _expenseRepository.createExpense(expenseWithReceipt);
+    } catch (e) {
+      _errorService.logError('ExpenseService', 'Erreur création expense: $e');
+      rethrow;
+    }
+  }
+
+  // Mise à jour avec validation
+  Future<void> updateExpenseWithValidation(Expense expense, File? newReceiptImage) async {
+    try {
+      _validateExpenseData(expense);
+      
+      // Gérer le nouvel upload si nécessaire
+      String? receiptUrl = expense.receiptUrl;
+      if (newReceiptImage != null) {
+        receiptUrl = await _storageService.uploadReceiptImage(
+          expense.groupId,
+          newReceiptImage,
+        );
+      }
+      
+      final expenseWithReceipt = expense.copyWith(
+        receiptUrl: receiptUrl,
+        editedAt: DateTime.now(),
+        isEdited: true,
+      );
+      
+      await _expenseRepository.updateExpense(expenseWithReceipt);
+    } catch (e) {
+      _errorService.logError('ExpenseService', 'Erreur update expense: $e');
+      rethrow;
+    }
+  }
+
+  // Validation des données
+  void _validateExpenseData(Expense expense) {
+    if (expense.description.trim().isEmpty) {
+      throw Exception('La description est requise');
+    }
+
+    if (expense.amount <= 0) {
+      throw Exception('Le montant doit être positif');
+    }
+
+    if (expense.splits.isEmpty) {
+      throw Exception('Au moins un participant est requis');
+    }
+
+    final totalSplits = expense.splits.fold(0.0, (sum, split) => sum + split.amount);
+    if ((totalSplits - expense.amountInEur).abs() > 0.01) {
+      throw Exception('La somme des répartitions ne correspond pas au montant total');
+    }
+  }
+}
\ No newline at end of file
diff --git a/lib/services/group_service.dart b/lib/services/group_service.dart
index 8190cab..7eaeb72 100644
--- a/lib/services/group_service.dart
+++ b/lib/services/group_service.dart
@@ -1,5 +1,5 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
-import 'package:travel_mate/data/models/group.dart';
+import 'package:travel_mate/models/group.dart';
 import 'package:travel_mate/services/error_service.dart';
 
 class GroupService {
diff --git a/lib/services/message_service.dart b/lib/services/message_service.dart
index 35c107e..21dd0e7 100644
--- a/lib/services/message_service.dart
+++ b/lib/services/message_service.dart
@@ -1,4 +1,4 @@
-import '../data/models/message.dart';
+import '../models/message.dart';
 import '../repositories/message_repository.dart';
 import 'error_service.dart';
 
diff --git a/lib/services/storage_service.dart b/lib/services/storage_service.dart
new file mode 100644
index 0000000..d7c6761
--- /dev/null
+++ b/lib/services/storage_service.dart
@@ -0,0 +1,214 @@
+import 'dart:io';
+import 'dart:typed_data';
+import 'package:firebase_storage/firebase_storage.dart';
+import 'package:path/path.dart' as path;
+import 'package:image/image.dart' as img;
+import 'error_service.dart';
+
+class StorageService {
+  final FirebaseStorage _storage;
+  final ErrorService _errorService;
+
+  StorageService({
+    FirebaseStorage? storage,
+    ErrorService? errorService,
+  }) : _storage = storage ?? FirebaseStorage.instance,
+       _errorService = errorService ?? ErrorService();
+
+  /// Upload d'une image de reçu pour une dépense
+  Future<String> uploadReceiptImage(String groupId, File imageFile) async {
+    try {
+      // Validation du fichier
+      _validateImageFile(imageFile);
+
+      // Compression de l'image
+      final compressedImage = await _compressImage(imageFile);
+
+      // Génération du nom de fichier unique
+      final fileName = _generateReceiptFileName(groupId);
+
+      // Référence vers le storage
+      final storageRef = _storage.ref().child('receipts/$groupId/$fileName');
+
+      // Métadonnées pour optimiser le cache et la compression
+      final metadata = SettableMetadata(
+        contentType: 'image/jpeg',
+        customMetadata: {
+          'groupId': groupId,
+          'uploadedAt': DateTime.now().toIso8601String(),
+          'compressed': 'true',
+        },
+      );
+
+      // Upload du fichier
+      final uploadTask = storageRef.putData(compressedImage, metadata);
+
+      // Monitoring du progrès (optionnel)
+      uploadTask.snapshotEvents.listen((TaskSnapshot snapshot) {
+        final progress = (snapshot.bytesTransferred / snapshot.totalBytes) * 100;
+        _errorService.logInfo('StorageService', 'Upload progress: ${progress.toStringAsFixed(1)}%');
+      });
+
+      // Attendre la completion
+      final snapshot = await uploadTask;
+
+      // Récupérer l'URL de téléchargement
+      final downloadUrl = await snapshot.ref.getDownloadURL();
+
+      _errorService.logSuccess('StorageService', 'Image uploadée avec succès: $fileName');
+      return downloadUrl;
+
+    } catch (e) {
+      _errorService.logError('StorageService', 'Erreur upload image: $e');
+      rethrow;
+    }
+  }
+
+  /// Supprimer une image de reçu
+  Future<void> deleteReceiptImage(String imageUrl) async {
+    try {
+      if (imageUrl.isEmpty) return;
+
+      // Extraire la référence depuis l'URL
+      final ref = _storage.refFromURL(imageUrl);
+      await ref.delete();
+
+      _errorService.logSuccess('StorageService', 'Image supprimée avec succès');
+    } catch (e) {
+      _errorService.logError('StorageService', 'Erreur suppression image: $e');
+      // Ne pas rethrow pour éviter de bloquer la suppression de la dépense
+    }
+  }
+
+  /// Compresser une image pour optimiser le stockage
+  Future<Uint8List> _compressImage(File imageFile) async {
+    try {
+      // Lire l'image
+      final bytes = await imageFile.readAsBytes();
+      img.Image? image = img.decodeImage(bytes);
+
+      if (image == null) {
+        throw Exception('Impossible de décoder l\'image');
+      }
+
+      // Redimensionner si l'image est trop grande
+      const maxWidth = 1024;
+      const maxHeight = 1024;
+
+      if (image.width > maxWidth || image.height > maxHeight) {
+        image = img.copyResize(
+          image,
+          width: image.width > image.height ? maxWidth : null,
+          height: image.height > image.width ? maxHeight : null,
+          interpolation: img.Interpolation.linear,
+        );
+      }
+
+      // Encoder en JPEG avec compression
+      final compressedBytes = img.encodeJpg(image, quality: 85);
+      
+      _errorService.logInfo('StorageService', 
+        'Image compressée: ${bytes.length} → ${compressedBytes.length} bytes');
+
+      return Uint8List.fromList(compressedBytes);
+    } catch (e) {
+      _errorService.logError('StorageService', 'Erreur compression image: $e');
+      // Fallback: retourner l'image originale si la compression échoue
+      return await imageFile.readAsBytes();
+    }
+  }
+
+  /// Valider le fichier image
+  void _validateImageFile(File imageFile) {
+    // Vérifier que le fichier existe
+    if (!imageFile.existsSync()) {
+      throw Exception('Le fichier image n\'existe pas');
+    }
+
+    // Vérifier la taille du fichier (max 10MB)
+    const maxSizeBytes = 10 * 1024 * 1024; // 10MB
+    final fileSize = imageFile.lengthSync();
+    if (fileSize > maxSizeBytes) {
+      throw Exception('La taille du fichier dépasse 10MB');
+    }
+
+    // Vérifier l'extension
+    final extension = path.extension(imageFile.path).toLowerCase();
+    const allowedExtensions = ['.jpg', '.jpeg', '.png', '.webp'];
+    if (!allowedExtensions.contains(extension)) {
+      throw Exception('Format d\'image non supporté. Utilisez JPG, PNG ou WebP');
+    }
+  }
+
+  /// Générer un nom de fichier unique pour un reçu
+  String _generateReceiptFileName(String groupId) {
+    final timestamp = DateTime.now().millisecondsSinceEpoch;
+    final random = DateTime.now().microsecond;
+    return 'receipt_${groupId}_${timestamp}_$random.jpg';
+  }
+
+  /// Upload multiple d'images (pour futures fonctionnalités)
+  Future<List<String>> uploadMultipleImages(
+    String groupId, 
+    List<File> imageFiles,
+  ) async {
+    final uploadTasks = imageFiles.map((file) => uploadReceiptImage(groupId, file));
+    return await Future.wait(uploadTasks);
+  }
+
+  /// Récupérer les métadonnées d'une image
+  Future<FullMetadata?> getImageMetadata(String imageUrl) async {
+    try {
+      final ref = _storage.refFromURL(imageUrl);
+      return await ref.getMetadata();
+    } catch (e) {
+      _errorService.logError('StorageService', 'Erreur récupération metadata: $e');
+      return null;
+    }
+  }
+
+  /// Nettoyer les images orphelines d'un groupe
+  Future<void> cleanupGroupImages(String groupId) async {
+    try {
+      final groupRef = _storage.ref().child('receipts/$groupId');
+      final listResult = await groupRef.listAll();
+
+      for (final ref in listResult.items) {
+        // Vérifier l'âge du fichier
+        final metadata = await ref.getMetadata();
+        final uploadDate = metadata.timeCreated;
+        
+        if (uploadDate != null) {
+          final daysSinceUpload = DateTime.now().difference(uploadDate).inDays;
+          
+          // Supprimer les fichiers de plus de 30 jours sans dépense associée
+          if (daysSinceUpload > 30) {
+            await ref.delete();
+            _errorService.logInfo('StorageService', 'Image orpheline supprimée: ${ref.name}');
+          }
+        }
+      }
+    } catch (e) {
+      _errorService.logError('StorageService', 'Erreur nettoyage images: $e');
+    }
+  }
+
+  /// Calculer la taille totale utilisée par un groupe
+  Future<int> getGroupStorageSize(String groupId) async {
+    try {
+      final groupRef = _storage.ref().child('receipts/$groupId');
+      final listResult = await groupRef.listAll();
+      
+      int totalSize = 0;
+      for (final ref in listResult.items) {
+        final metadata = await ref.getMetadata();
+        totalSize += metadata.size ?? 0;
+      }
+      
+      return totalSize;
+    } catch (e) {
+      _errorService.logError('StorageService', 'Erreur calcul taille storage: $e');
+      return 0;
+    }
+  }
+}
\ No newline at end of file
diff --git a/lib/services/trip_service.dart b/lib/services/trip_service.dart
index 2d90461..6597ebe 100644
--- a/lib/services/trip_service.dart
+++ b/lib/services/trip_service.dart
@@ -1,6 +1,6 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:travel_mate/services/error_service.dart';
-import '../data/models/trip.dart';
+import '../models/trip.dart';
 
 class TripService {
   final _errorService = ErrorService();