GOV.UK Self Assessment Tax Calculator review

Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

GOV.UK’s Self Assessment Tax Calculator is a free web tool from HM Revenue & Customs for estimating Income Tax for the 2025 to 2026 tax year. For self-employed users, it also estimates Class 4 National Insurance. It is aimed at people who want a broad estimate that brings several income streams into one calculation, including self-employment profits, rental income, State or occupational pension income, and paid employment. Users enter estimated weekly or monthly income, so it can support an early view of a tax bill rather than a calculation based on finalized figures.

Its mixed-income coverage is the main reason to consider it. Many sole traders also have employment, pension, or property income, and the calculator includes each of those sources in its estimate alongside self-employment profits. The scope is still specific: it focuses on Income Tax and Class 4 National Insurance, and the estimate assumes the standard Personal Allowance. That assumption matters for anyone whose circumstances make the standard allowance inapplicable, so the result should be treated as an estimate rather than a complete account of an individual’s tax position.

The exclusions narrow its fit further. It does not account for the High Income Child Benefit Charge, savings and investment income, or payments already made toward the next tax bill. Someone with those factors may need a different way to calculate their overall liability. For a UK self-employed person with mixed income who wants a free, web-based estimate for 2025–26, this is a focused starting point; it is less suitable as a complete tax-planning tool for more complicated income or payment situations.

GOV.UK Self Assessment Tax Calculator pros and cons

• Where it wins
  • Estimates Income Tax for the 2025 to 2026 tax year
  • Includes Class 4 National Insurance for self-employed users
  • Combines self-employment, rental, pension, and employment income
• Where it doesn't
  • Assumes the standard Personal Allowance
  • Does not account for savings and investment income
  • Excludes the High Income Child Benefit Charge and amounts already paid

GOV.UK Self Assessment Tax Calculator fact sheet, pricing and score →

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Last updated 5 Oct 2026 · How we research and update