Estimate your Self Assessment tax and National Insurance
See what you'll owe in Income Tax and National Insurance for a UK tax year, broken down line by line in the same order HMRC uses. It all runs in your browser, so nothing you type is saved or sent anywhere.
See every band
Basic, higher and additional rate each get their own line, with the rate and the amount, so you can see where every pound of tax comes from.
Correct for the year
Each year has its own bands, allowances and NI rates. 2022-23 even uses that year's blended Class 4 rates.
Nothing is saved
No account, no login, no database. The maths happens on your device and disappears when you close the tab.
What this estimator does
Filing a Self Assessment return can feel like a black box: you put numbers in, and weeks later a bill comes out. This tool opens the box. Enter what you earned and it works through the same steps HMRC does: total income, your Personal Allowance, the income that's actually taxable, then tax at each band, and Class 2 and Class 4 National Insurance if you're self-employed.
It's built for the self-employed and for anyone who wants to sanity-check a figure before the January deadline. It won't file anything for you, and it deliberately doesn't try to look like an official HMRC document. It's a calculator, plainly labelled as an estimate, so you can plan with a realistic number instead of a guess.
Popular guides
- How Self Assessment tax is calculated, step by step: the full order of operations, with a worked example.
- Class 2 vs Class 4 National Insurance: what the self-employed actually pay, and the recent rate cuts.
- The Personal Allowance taper over £100k: why £1 of income can cost you 60p.
- How to legally reduce your tax bill: pensions, expenses and timing.
Frequently asked questions
Is this an official HMRC SA302?
No. SA302 Estimate is an independent calculator. It gives you an estimate of your tax, not an official document. HMRC produces the real SA302 from your filed return, and only that version should be sent to a mortgage lender.
Which tax years can I estimate?
You can estimate 2022-23, 2023-24, 2024-25 and 2025-26. Each year uses its own tax bands, allowances and National Insurance rates, because these change from year to year.
Does it include National Insurance?
Yes. If you enter self-employment profit, the estimate includes Class 4 National Insurance across its bands and shows Class 2, which for 2024-25 and 2025-26 is treated as paid rather than charged.
Is my information saved anywhere?
No. Every figure is processed in your own browser. Nothing is sent to a server, written to a database, or stored. Close the tab and it is gone. There is no account and no login.
How accurate are the figures?
The engine uses England and Northern Ireland rates and has been cross-checked against real HMRC tax calculations and published figures for each year. It is still an estimate and does not cover every situation, so confirm important numbers with HMRC or an accountant.