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…