DEV3 India Income Tax Calculator FY 2026-27 — Source Code (React + Tailwind)

Source code of the DEV3 India Income Tax Calculator FY 2026-27, an Indian income tax calculator for FY 2026-27 that compares the old and new regimes with slabs, standard deduction, 87A rebate, marginal relief, surcharge and cess.

Download: buy a licence and the ZIP is waiting in Account → Downloads. Try it live: https://dev3.tech/tools/india-income-tax-calculator shows the finished tool running.

What is in the download

• A standalone Vite + React + TypeScript + Tailwind CSS project: src/tool holds the tool, shared pieces sit beside it
• package.json with exact versions plus a lockfile, so npm ci works
• README.md (run, build, embed in Next.js or plain React) and an MIT LICENSE

What the code does

• Side-by-side old and new regime results with a verdict
• Rebate, surcharge and marginal relief logic
• Deduction inputs: 80C, 80D, HRA, home loan interest, NPS
• Rules constants in one shared file with the date they were last checked

Tech stack

React 19, TypeScript, Vite, Tailwind CSS 4.

Install and customise

The How to install and How to use tabs list the steps. In short: unzip, npm ci, npm run dev, then copy the tool folder into your own app if you want to embed it.

Good to know

• A browser-only tool: there is no backend or database in the code.
• Covers resident individuals below 60 and ordinary income only; no capital gains special rates or senior citizen slabs.