SIP & Mutual Fund Backtester (India)

A production-grade MVP for backtesting Indian mutual fund SIP investments with tax calculations, FD comparison, and portfolio rebalancing suggestions.

🎯 Purpose

This tool helps Indian retail investors:

Analyze historical SIP returns for mutual funds
Calculate post-tax returns (LTCG/STCG)
Compare MF returns with Fixed Deposits
Get rule-based portfolio rebalancing suggestions

🏗️ Architecture

┌─────────────────────────────────────────────────────────────┐
│                        Frontend                              │
│  ┌──────────────┐ ┌──────────────┐ ┌──────────────┐         │
│  │ Input Form   │ │  Results     │ │  Rebalance   │         │
│  │              │ │  Dashboard   │ │  Panel       │         │
│  └──────────────┘ └──────────────┘ └──────────────┘         │
│         React + Vite (Port 5173)                            │
└─────────────────────────────────────────────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│                     Backend API                              │
│  ┌──────────────┐ ┌──────────────┐ ┌──────────────┐         │
│  │ /api/funds   │ │/api/simulate │ │/api/rebalance│         │
│  └──────────────┘ └──────────────┘ └──────────────┘         │
│         FastAPI + Uvicorn (Port 8000)                       │
└─────────────────────────────────────────────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│               Financial Calculation Engine                   │
│  ┌────────────┐ ┌──────────┐ ┌──────────┐ ┌──────────────┐  │
│  │SIP Engine  │ │ Returns  │ │ Taxation │ │ Comparison   │  │
│  │            │ │CAGR/XIRR │ │LTCG/STCG │ │ MF vs FD     │  │
│  └────────────┘ └──────────┘ └──────────┘ └──────────────┘  │
└─────────────────────────────────────────────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│                    Data Layer                                │
│          Versioned CSV files (data/nav/)                     │
└─────────────────────────────────────────────────────────────┘

📊 Financial Assumptions

Tax Model (FY 2024-25)

Category	Type	Rate	Notes
Equity Funds	LTCG (>1 year)	12.5%	Exempt up to ₹1.25L annually
Equity Funds	STCG (<1 year)	20%	Full gains taxable
Debt Funds	All	Slab Rate	No indexation (post-April 2023)
Fixed Deposits	Interest	Slab Rate	Fully taxable

FD Rates Used

1 year: 6.5%
2-3 years: 7.0%
5+ years: 7.25%

Rebalance Targets

Horizon	Equity	Debt
Short (<3 yrs)	20%	80%
Medium (3-7 yrs)	50%	50%
Long (>7 yrs)	80%	20%

📁 Data Sources

Sample data included for demonstration purposes.

For production use, data can be sourced from:

AMFI India (amfiindia.com) - Official NAV data
Fund house websites - Historical NAV disclosures
Value Research / Morningstar - Third-party aggregators

NAV CSV Format

date,fund_id,fund_name,nav,fund_type,expense_ratio
2024-01-02,HDFC_FLEXI,HDFC Flexicap Fund,525.45,equity,1.75

🚀 Running Locally

Prerequisites

Python 3.11+
Node.js 18+
pip / npm

Backend Setup

cd backend
python -m venv venv
venv\Scripts\activate  # Windows
pip install -r requirements.txt
uvicorn app.main:app --reload

Backend runs at: http://localhost:8000

Frontend Setup

cd frontend
npm install
npm run dev

Frontend runs at: http://localhost:5173

Running Tests

cd backend
pip install pytest httpx
pytest tests/ -v

🌐 Deployment

Free Hosting Options

Backend (Python/FastAPI)

Render.com (free tier)
Railway.app
Fly.io

Frontend (React)

Vercel
Netlify
GitHub Pages (for static build)

Environment Variables

# Backend
CORS_ORIGINS=https://your-frontend.vercel.app

# Frontend (if not using proxy)
VITE_API_URL=https://your-backend.onrender.com

⚠️ Limitations

Historical data only - Cannot predict future returns
Sample data - MVP includes demo data; connect real NAV feeds for production
Tax simplifications - Does not handle:
- Grandfathering rules
- Multiple financial years in one redemption
- Set-off of losses
No real-time data - NAV data is static CSVs
Single fund simulation - Multi-fund portfolio analysis not implemented

📜 Disclaimer

⚠️ This is an educational tool for historical analysis only.

Past performance does not guarantee future returns
Tax calculations are estimates based on FY 2024-25 rules
Always consult a SEBI-registered investment advisor before investing
Verify calculations independently before making financial decisions

🧪 Test Coverage

Module	Tests
SIP Engine	Date generation, unit calculation, expense drag
Returns	CAGR accuracy, XIRR convergence, volatility
Taxation	Equity/Debt classification, LTCG/STCG edge cases
API	Endpoints, response schemas, error handling

📝 License

MIT License - Free for personal and commercial use.

Built with ❤️ for Indian retail investors.

SIP Backtester