Rupee Finance Toolkit — Calculator App

A complete, offline-first Android finance calculator app built specifically for the Indian market. Covers EMI, GST, salary breakdowns, income tax (FY 2024-25), SIP, compound interest, NPV/IRR, discount, ROI, and more — all in Indian Rupee format (lakh/crore) with correct Indian tax rules, EPF, CGST/SGST/IGST splits, and Section 87A rebate. Clean Material Design UI, no ads, no internet required, and ready to publish on Google Play, Amazon App Store, or any Android platform.

Rupee Finance Toolkit is a production-ready Android app source code (Kotlin + Jetpack) designed from the ground up for Indian users. India has a unique financial landscape — lakh/crore number formatting, GST with CGST/SGST/IGST splits, EPF at 12% of basic salary, professional tax varying by state, and income tax rules that change every budget. Generic finance apps get these wrong. This app gets them right.

Every calculator is self-contained with its own activity, formula reference, worked examples, FAQs, and real-life use cases — so end users understand their finances, not just the answer. The codebase is modular and clean, making it straightforward to add new calculators, rebrand, or integrate ads.

Whether you’re building a product for salaried professionals who want to understand their take-home pay, small business owners who need GST breakdowns, or investors planning SIPs — this source code gives you a complete, tested, India-specific financial calculator that is ready to ship.

All amounts display in Indian format (₹1,00,000 not ₹100,000). All tax rules are updated for FY 2024-25 including the revised new regime slabs, standard deduction of ₹75,000, and Section 87A rebate for income up to ₹7 lakh. Professional tax defaults are correct for Maharashtra, Karnataka, West Bengal, Tamil Nadu, and Gujarat, with a note for zero-PT states like Delhi and UP.

CALCULATORS INCLUDED

1. EMI / Loan Calculator — Reducing-balance EMI formula: P × r × (1+r)^{n / ((1+r)}n − 1) — Inputs: Principal, annual interest rate, tenure in months — Outputs: Monthly EMI, total interest payable, total amount payable — Covers home loans, car loans, personal loans, education loans

2. GST Calculator — All 5 Indian GST slabs: 0%, 5%, 12%, 18%, 28% — GST-exclusive (add GST to base) and GST-inclusive (extract GST from total) modes — Automatic CGST/SGST split for intra-state and IGST for inter-state supply — GST registration threshold info (₹40 lakh goods / ₹20 lakh services)

3. Salary / CTC Calculator — User-editable Basic Salary % (not hardcoded — pulled from payslip) — Employee PF deduction at configurable rate (default 12% of basic) — Professional tax input (state-specific, defaults to ₹200/month) — TDS / income tax monthly deduction input — Outputs: Gross monthly, net take-home, weekly, daily (250 working days), hourly

4. Income Tax Estimator (FY 2024-25 New Regime) — Correct tax slabs: 0% up to ₹3L, 5% ₹3–7L, 10% ₹7–10L, 15% ₹10–12L, 20% ₹12–15L, 30% above ₹15L — Standard deduction of ₹75,000 automatically applied — Section 87A rebate: zero tax if net taxable income ≤ ₹7 lakh — Surcharge and cess calculation included

5. Simple Interest Calculator — Formula: SI = P × R × T / 100 — Total amount and interest breakdown

6. Compound Interest Calculator — Formula: A = P × (1 + r/n)^{(n×t) — Configurable compounding frequency: annual, half-yearly, quarterly, monthly}

7. SIP / Investment Planner — Future value with monthly contributions — Formula: FV = PV × (1+r)n + PMT × ((1+r)^n − 1) / r — Ideal for mutual fund SIP planning

8. Discount Calculator — Discount amount and final discounted price — Useful for retail and e-commerce pricing

9. Profit / Margin Calculator — Gross profit margin, net profit, ROI — Revenue and COGS inputs

10. NPV / IRR Calculator — Net Present Value with configurable discount rate and multiple cash flows — IRR using bisection method with 1000-iteration convergence

11. Payback Period Calculator — Initial investment vs annual cash inflow ratio

12. Inflation Calculator — Inflation-adjusted future value — Real purchasing power (present value after inflation)

13. Currency Converter — Converts between currencies using user-supplied exchange rates — Useful for import/export businesses and NRI users