Self-Assessment Tax Calculator 2025-26

Estimate your self-assessment tax bill including income tax, National Insurance Class 2 and Class 4 for self-employed.

Last updated: April 2026 · Source: GOV.UK — Self Assessment tax returns

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Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Self Assessment is the system HMRC uses to collect income tax from people whose tax is not fully deducted at source. This includes the self-employed, company directors, landlords, and anyone with income over £150,000 or significant untaxed income.

This calculator estimates your Self Assessment tax bill by combining income tax, Class 2 NI (£3.45/week if profits exceed £12,570), Class 4 NI (6% on profits between £12,570 and £50,270, then 2% above) and any student loan repayments.

Payment on Account may apply: if your tax bill is over £1,000 and less than 80% was collected at source, you may need to make two advance payments (each 50% of the previous year's bill) on 31 January and 31 July.

Example: Self-employed, £55,000 profit

  1. Income tax: £8,432 (PA + Basic + partial Higher)
  2. Class 2 NI: £179.40 (52 weeks × £3.45)
  3. Class 4 NI: £2,264 + £94.60 = £2,358.60
  4. Total Self Assessment bill: £10,970

Source: GOV.UK — Self Assessment tax returns

Frequently Asked Questions

Who needs to file a Self Assessment tax return?
You must file a Self Assessment return if you are self-employed, a company director, earn over £150,000, have untaxed income (e.g. rental income, savings interest above your allowance), or need to claim tax reliefs. HMRC will notify you if you need to file.
What is the deadline for Self Assessment?
The deadline for online Self Assessment returns is 31 January following the end of the tax year. For example, the 2025/26 return must be filed online by 31 January 2027. Paper returns must be filed by 31 October.