SA100 (Self Assessment Tax Return)
UK tax glossary · Last reviewed: April 2026
The SA100 is the core Self Assessment return. It covers employment income, self-employment income (via SA103), property income (SA105), dividends, savings interest, capital gains (SA108), and various reliefs and allowances. Most people file online rather than on paper.
The online filing deadline for 2025/26 is 31 January 2027. The paper deadline is 31 October 2026. HMRC automatically calculates your tax liability from the figures you enter, so no arithmetic is required.
Supplementary pages (SA102 for employment, SA103 for self-employment, SA105 for property, SA108 for capital gains) attach to the main SA100. Many taxpayers only need the SA100 itself for simpler income types.
Common questions
Do I need to file an SA100 every year once registered?
Yes, unless HMRC tells you otherwise. Even if you had no additional tax to pay, you should file or request to be removed from Self Assessment if your circumstances have changed.
Can I file a Self Assessment return early?
Yes. You can file from 6 April after the tax year ends. Filing early does not mean paying early — tax is still due 31 January — but it gives you certainty about your liability sooner.
Related resources
TaxHelper provides general information based on published HMRC rates and guidance. It is not regulated financial or tax advice. For decisions involving significant sums, complex circumstances, or if you are unsure, speak to a qualified accountant or HMRC directly.