Self Assessment Tax Calculator UK 2026/27
Self-employed or earning outside of PAYE? Estimate your Self Assessment tax bill for 2026/27 — including payments on account — so you're not caught short when the deadline hits. This self assessment tax calculator estimates your bill including Class 4 National Insurance and payments on account — effectively a self employed tax calculator.
- Enter income from all sources.
- See your total tax bill and payments on account.
| Amount | |
|---|---|
| Total taxable income | - |
| Income tax | - |
| Class 2 NI | - |
| Class 4 NI | - |
| Total tax bill | - |
| 1st payment on account (31 Jan) | - |
| 2nd payment on account (31 Jul) | - |
| Save per month | - |
Self Assessment is how HMRC collects tax from the self-employed, landlords, company directors and anyone with untaxed income. The bill often comes as a shock because it includes two things people forget: Class 4 National Insurance and payments on account. This estimator gives you a realistic figure before you file.
What your Self Assessment bill includes
A typical bill combines:
- Income tax on your total taxable income, after the £12,570 allowance
- Class 4 National Insurance — 6% on profits between £12,570 and £50,270, then 2% above
- Class 2 National Insurance — no longer compulsory since 2024/25: treated as paid if your profits are at least £7,105, otherwise voluntary at £3.65 a week to protect your State Pension record
- Tax on dividends, rental income or savings, if applicable
Payments on account explained
If your bill exceeds £1,000, HMRC usually requires payments on account — advance payments towards next year's tax, each equal to half your previous bill. This is why first-year bills often feel double the expected amount. You pay on 31 January and 31 July, with a balancing payment the following January. If your income has dropped, you can ask to reduce them.
Deadlines and penalties
The online filing deadline is 31 January following the end of the tax year. Late filing triggers an immediate £100 penalty, with further charges after 3, 6 and 12 months, plus interest on unpaid tax. Registering late is also a common and avoidable error — you must register by 5 October after your first tax year.
Estimate your bill above, then plan your take-home with the take-home pay calculator.