About SA302 Estimate
SA302 Estimate is a free, independent calculator for working out roughly how much Income Tax and National Insurance a self-employed person owes under UK Self Assessment. It was built because the gap between "I earned this" and "I owe this" is wider than it should be, and most people only find out the number when the bill lands.
What we are
We're an independent tool, not a tax authority and not an accountancy firm. The calculator uses the published tax bands, allowances and National Insurance rates for each supported year (2022-23 through 2025-26) and shows the working in the same order HMRC's own calculation follows, so the output is easy to check against a real tax calculation.
What we are not
We are not HMRC and we are not affiliated with GOV.UK. We don't produce official documents, we can't see your tax record, and we can't file anything on your behalf. An estimate from this site is not an official SA302 and should not be sent to a mortgage lender in place of one. When money or a mortgage depends on the exact figure, use the real calculation from HMRC or ask a qualified accountant.
Why it's free
The site is supported by advertising. That keeps the calculator free to use and means we don't need your email address, an account, or any of your financial details stored on a server. The maths runs in your browser and nothing you enter is saved or sent to us.
Accuracy
We take the numbers seriously and cross-check each year's rates against published figures and real tax calculations. Tax is full of edge cases, though (Scottish and Welsh rates, marriage allowance, student loans, Gift Aid, capital gains and more), and a general estimator can't cover every one. If you spot something that looks off, please tell us.