Independent software studio

Software for people who want to actually understand their money.

Atlas Foundry builds small, premium tools that explain themselves — starting with a UK Self Assessment tax calculator that shows its working, not just its total.

Visit the Etsy shop See how it works

Offline-first — no accounts, no servers Built for Chrome, Safari, Edge, Firefox

Atlas Foundry dashboard showing a tax liability breakdown across four charts

Every figure explained — not just calculated

See it in action

Atlas Foundry in 45 seconds

A quick walkthrough of the calculator, start to finish.

What is Atlas Foundry?

Atlas Foundry is a small, independent studio building financial software the way we think it should be built: plain-English, offline, and honest about its own limits. No dashboards designed to keep you scrolling, no subscriptions billed quietly every month, no data leaving your device.

Everything we make is a proper download — open one file, and it works. We'd rather ship one tool done properly than ten done halfway.

IndependentSelf-funded, no investors dictating the roadmap.

Offline-firstYour figures never touch a server we run.

Plainly explainedEvery number traceable back to a reason.

Available now on Etsy

The Self Assessment Tax Calculator

Our flagship tool: a complete, offline UK Self Assessment calculator for individuals with employment, self-employment, property, savings, dividends, and capital gains income. Now available in our Etsy shop.

Every step, shown working

Not just a number — the full calculation, laid out in the same order HMRC works through it, from turnover down to what you actually owe.

13 calculation steps, expandable for full detail
Matches HMRC's own Self Assessment box numbers
Exportable as a record for your accountant

Tax Breakdown screen listing thirteen numbered calculation steps

Reliefs calculated automatically

Higher and additional-rate pension and Gift Aid relief is easy to under-claim by hand. Atlas Foundry works out exactly what's owed, and shows you why.

Pension and Gift Aid relief, worked automatically
Marriage Allowance, HICBC and Student Loan handled
A "What If?" planner for changes you're considering

Pension and Gift Aid relief screen showing a grossed-up contribution and additional relief claimable

✓

Truly offline

Open one file in your browser — no internet connection needed, ever.

✓

No account, no subscription

Pay once, keep it — the same principle behind everything we build.

✓

Light & dark mode

Matches your system automatically, or choose your own.

✓

Save, export & print

Your work saves locally, exports as a project file, or prints as a PDF.

✓

Built for every major browser

Chrome, Safari, Edge and Firefox on Mac and Windows.

✓

Nothing hidden

Unsupported scenarios are flagged clearly, never silently guessed.