I've been building Instant Receipts — a receipt scanning and BAS prep app for Australian sole traders — and as part of that I built a set of free calculators that live on the main site.
Recently I extracted them into a standalone static site on GitHub Pages so they work without any framework, server or build step.
What's included
Six tools, all pure HTML/CSS/JS:
- GST Calculator — add 10% GST to a price, or remove it using the 1/11th rule
- BAS Calculator — work out G1, 1A and 1B for your Business Activity Statement
- Sole Trader Tax Calculator — income tax, Medicare levy, HELP repayment and take-home pay
- Mileage Calculator — ATO cents per km deduction (91¢/km for 2026-27)
- Work From Home Calculator — ATO 70¢/hour fixed rate deduction
- Invoice Generator — tax invoice with ABN, GST per line, download as PDF
Why pure HTML/JS
No npm install. No build step. No framework. Just open the file and it works.
The calculators run entirely in the browser — nothing is sent to a server, nothing is stored. For a tool that asks people to enter their income and expenses, that felt like the right call.
The GitHub Pages version is at instant-receipts-pty-ltd.github.io/australian-calculators if you want to see the source.
Australian tax is surprisingly specific
The GST 1/11th rule, BAS labels, the Small Business Income Tax Offset, ATO cents per km rates — none of this exists in any international calculator library. Had to build it all from scratch with the ATO's own documentation.
Happy to answer questions about the Australian tax side or the vanilla JS approach.
