The SA100: Main Return Form
The SA100 is HMRC's main Self Assessment tax return form. It covers basic personal details, income from employment, pensions, savings and investments, along with claims for reliefs and deductions. It is the starting point for all UK Self Assessment returns.
Most people filing online never see the SA100 as a physical document โ HMRC's online portal and most tax software present the same questions in a different format. But understanding the structure helps when working with an accountant or completing supplementary pages.
Supplementary Pages You May Need
| Form | Required For |
|---|---|
| SA103S (Short) | Self-employment with turnover under ยฃ85,000 |
| SA103F (Full) | Self-employment with turnover above ยฃ85,000 |
| SA105 | UK property income |
| SA106 | Foreign income |
| SA108 | Capital gains |
| SA101 | Additional income (pensions, trusts, etc.) |
Source: HMRC / gov.uk ยท Rates correct for 2025/26 tax year.
Most self-employed freelancers need the SA100 plus either SA103S or SA103F depending on their turnover. The forms are available on the gov.uk website if filing on paper, or appear automatically in the online return when you select the appropriate income types.
SA100 vs Online Filing
The paper SA100 must be submitted by 31 October. The online equivalent โ filed through HMRC's portal or tax software โ has a later deadline of 31 January, which is why the vast majority of filers now use the online system. The information collected is identical; the format and deadline differ.