Expense Expert is a full-stack expense sharing and settlement platform for trips, roommates, events, and teams. It helps groups track spending, split costs flexibly, and settle with the minimum number of transfers.
Landing Page
Main Dashboard
Split View
Analytics Dashboard
- Real-time multi-user session updates.
- Smart settle-up recommendations.
- Advanced split logic for real-world scenarios.
- Rich analytics and what-if simulation.
- Easy sharing and export workflows.
- Create a session with trip/group name.
- Add members one by one using chip-style input.
- Join an existing session using session code.
- Live member presence tracking with SSE.
- Activity feed for expense and settlement events.
- Add and delete expenses.
- Payer tracking with paid-by payload.
- Split type badges in expense list.
- Expandable per-expense split breakdown.
- Inline validation in add-expense flow.
Unified backend split engine supports 4 modes:
- EQUAL: even split with remainder handling.
- EXACT: fixed amount per member.
- PERCENTAGE: split by percentage values.
- SHARE: split by integer share units.
Validation rules:
- EXACT total must match expense amount (tolerance 0.01).
- PERCENTAGE total must be 100 (tolerance 0.01).
- SHARE values must be positive integers.
- Session member integrity is enforced for split and payer data.
Structured backend validation response:
{
"message": "Exact split total does not match expense amount.",
"expected": 1000.00,
"actual": 700.00,
"delta": 300.00
}- Net balance view per member.
- Optimized settle-up suggestions.
- Mark settlement payments as partial or complete.
- Payment tracking visible in settle-up panel.
- What-if simulator to preview the impact of a hypothetical expense.
- Analytics dashboard with:
- category breakdown,
- member spending,
- fairness/health indicators,
- trip-level summary metrics.
- Shareable session links.
- WhatsApp-friendly settlement summary copy.
- PDF export endpoint integration.
- Premium, animated UI with Framer Motion and GSAP.
- Smooth scrolling using Lenis.
- Reusable shadcn-style UI primitives.
- In-app name capture for presence (replaces browser prompt).
Settlement optimization uses a greedy debtor-creditor matching strategy to reduce transaction count.
1. Compute net balance for each member:
net = total_paid - total_owed
2. Split members into:
- debtors (net < 0)
- creditors (net > 0)
3. Repeatedly match largest debtor with largest creditor.
4. Transfer min(abs(debtor), creditor), update balances.
5. Continue until all balances reach zero.
- Frontend: React, Vite, Tailwind CSS, Framer Motion, GSAP, Lenis, Axios, React Router.
- UI Layer: Custom shadcn-style primitives (Button, Card, Input, Badge).
- Backend: Java 21, Spring Boot, Maven.
- Database: PostgreSQL.
- Realtime: Server-Sent Events (SSE).
- Expense_Expert: Spring Boot backend.
- frontend: React frontend.
- UI_REFACTOR_PLAN.md: UI design and migration planning notes.
- Node.js 18+
- Java 21+
- Maven 3.9+
- PostgreSQL 14+
git clone https://github.com/Team-Zemo/Expense_Expert.git
cd ExpenseUpdate Expense_Expert/src/main/resources/application.properties:
server.port=8080
spring.datasource.url=jdbc:postgresql://localhost:5432/expense_expert
spring.datasource.username=postgres
spring.datasource.password=your_password
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=truecd Expense_Expert
mvn clean install
mvn spring-boot:runBackend URL: http://localhost:8080
cd frontend
npm install
npm run devFrontend URL: http://localhost:5173
# backend tests
cd Expense_Expert
mvn test
# frontend production build
cd frontend
npm run build- Backward compatibility for legacy split JSON is maintained while new expenses are saved in normalized split-array structure.
- Split engine behavior is covered by tests in Expense_Expert/src/test/java/com/teamzemo/exp/SplitEngineTest.java.
- Core split processing lives in backend service utilities and ExpenseService orchestration.
Built by Team Zemo.