Self Assessment tax calculator for the self-employed
A free UK Self Assessment tax calculator that works out your Income Tax and Class 2 and Class 4 National Insurance, broken down line by line in the same order HMRC uses. Covers 2022-23 to 2025-26. It runs entirely 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.
Matched against real HMRC calculations
Each year has its own bands, allowances and NI rates, and the engine reproduces real HMRC tax calculations exactly. See every check figure.
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 to get your SA302 from HMRC: the exact menu path, previous years, and what to do if an accountant filed for you.
- SA302 vs Tax Year Overview: why lenders ask for both, and what happens if you send only one.
- 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.
Working out what you'll owe
- How much tax will I pay when self-employed?: what the bill actually comes to at different profit levels, with worked figures.
- Estimating your tax before you file: why it pays to know the number early, and how to get a reliable one.
- Estimating your 2025-26 tax: what changed for the current tax year and how to work yours out.
Frequently asked questions
Is this an official HMRC SA302?
No. Estimate My Tax 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 is tested against real HMRC tax calculations and matches them to the penny — for example a 2024-25 self-employed profit of £142,850 produces a total of £54,599.10, exactly as HMRC worked it out. Every check figure is published on the methodology page, along with an honest list of what the calculator does not cover (Scottish rates, student loans and the High Income Child Benefit Charge among them). It is still an estimate, so confirm important numbers with HMRC or an accountant.