About

This is a free, open-source UK tax calculator covering the five most common situations a UK earner finds themselves in: PAYE employee, Limited Company director, Umbrella contractor, IR35 inside vs outside, and Sole Trader / Self-Employed.

What it does

The calculation engine implements HMRC's PAYE Tax Table Routines specification (v24.0, February 2026) — the same document HMRC publishes for payroll software vendors. Every prescribed rounding direction (Free Pay rounded up to 1p, Taxable Pay rounded down to £1, final tax rounded down to 1p) is followed exactly, and outputs are cross-checked against HMRC's own reference vectors for tax years 2024/25, 2025/26 and 2026/27.

Who built it

A solo project by @loglux, a UK-resident developer with a registered company. The calculator is one of several small self-hosted tools the project's maintainer runs — it stays free for end users; future B2B widget licensing (separate from this free tier) is planned.

Why it exists

Most UK take-home calculators online are lead-gen funnels for accountancy services. The numbers are usually right for textbook scenarios but drift on edge cases — K-codes, marriage allowance, Scottish bands with non-Scottish dividends, contractor IR35 inside vs outside. This calculator aims to be the boring, accurate one: same engine HMRC's spec describes, no upselling, source code public.

Source code & contributions

The calculation engine and this site live in one repository at github.com/loglux/tax_calculator. Commit history is the source-of-truth changelog. Bug reports and PRs welcome via GitHub issues; no formal contribution process yet because traffic is small and quality is enforced by the test suite.

Disclaimer

This calculator is not financial or tax advice. See the full Terms of Use and Privacy Policy.