SA103 is the self-employment section of your Self Assessment tax return, and it comes in two versions. Use the short pages, SA103S, if your turnover was less than £90,000, or would have been over a full year. Use the full pages, SA103F, if your turnover was £90,000 or more or your business is more complicated, for example because your accounting period didn't line up with the tax year.
Everything below comes from HMRC's SA103S form and notes and the SA103F notes for the tax year 6 April 2025 to 5 April 2026, as of October 2026.
Short or full: the quick test
| Use SA103F (full) if any of these apply | Otherwise SA103S (short) |
|---|---|
| Turnover of £90,000 or more, or would have been over a full year | Turnover under £90,000 |
| Your accounting period ended before 31 March 2026 or wasn't 12 months long, or didn't end in the tax year | Accounts made up to a date from 31 March to 5 April 2026 |
| You have adjustment income because you changed accounting basis | No change of basis |
| You need to adjust profits chargeable to Class 4 NICs | No Class 4 adjustments |
| You were in HMRC's Managing Serious Defaulters programme in the year | Not in that programme |
A small detail on the short pages: in box 7, if your accounts ran up to 5 April 2026 you enter 05 04 2026. If the date is before 31 March 2026, unless you stopped trading, or after 5 April 2026, you must switch to the full pages.
The £1,000 trading allowance
Total receipts from self-employment and miscellaneous income of up to £1,000 are exempt from tax and don't need to be reported, unless they're from a connected party. If your receipts are over £1,000, you can either claim the allowance in box 10.1 against them or deduct your actual expenses and capital allowances. You can't do both, and you can't claim it on receipts from a connected party.
Why you might file SA103 even under £1,000
This is the part most people never hear about. HMRC's notes list reasons to complete the short pages even when the allowance covers you:
- You expect turnover above £1,000 next year: complete boxes 1 to 8.
- You want to pay Class 2 National Insurance voluntarily to build State Pension entitlement: boxes 1 to 8 and an X in box 36.
- You want to keep a record of self-employment, for example to support a Maternity Allowance claim: box 1 only.
- You want to claim Tax-Free Childcare based on self-employment income: boxes 1, 9, 10.1, 21, 28 and 31.
- You're a construction subcontractor claiming back tax deducted under CIS: boxes 1 to 8 and box 38.
More on the voluntary contributions is on the Class 2 National Insurance page.
Expenses on the short pages
If your annual turnover was below £90,000, you may put your total expenses as one figure in box 20 rather than splitting them across boxes 11 to 19. If you claimed the trading allowance in box 10.1, leave boxes 11 to 20 blank. Put an X in box 8 only if you used traditional accounting, also called the accruals basis, instead of cash basis. Simplified expenses use flat rates instead of actual costs, for business vehicles or for business use of your home, but not both of those home options; everything else is calculated the usual way.
Who doesn't pay Class 4 National Insurance
Put an X in box 37 only if you're exempt from Class 4 NICs. For 2025 to 2026 that means you reached State Pension age on or before 6 April 2025, you were under 16 on 6 April 2025, or you weren't resident in the UK for tax purposes during the tax year. Everyone else's Class 4 is worked out from the profit on these pages, which is why the full pages are needed when Class 4 profits have to be adjusted.
Filling in SA103S, step by step
- Describe the business and enter its start date if it started in the year, plus the end date of your accounts in box 7.
- Enter turnover in box 9 and any other business income in box 10.
- Either claim the £1,000 trading allowance in box 10.1 or enter expenses in boxes 11 to 20.
- Add capital allowances if you're entitled to them.
- Work out your net profit or loss, then complete the losses and National Insurance boxes.
- Attach the pages to your SA100 return.
Subcontractors should add up every deduction contractors made under the Construction Industry Scheme and put the total in box 38, because that's tax already paid that comes off the bill, or comes back as a refund.
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If you haven't told HMRC you're self-employed yet, the first step is to register as self-employed so you get a Unique Taxpayer Reference. If you don't think you need a return, the notes say you must tell HMRC by 31 January 2027 to avoid penalties.
The verdict
Most sole traders under £90,000 with accounts to 31 March or 5 April belong on the short pages, and they're quick. Check the box 7 date, choose between the £1,000 allowance and real expenses, and if you're below £1,000 but want State Pension credit or Tax-Free Childcare, file the short pages anyway.
Frequently asked questions
Should I use SA103S or SA103F?
Use SA103S if turnover was under £90,000 and your accounts are straightforward. Use SA103F if turnover was £90,000 or more, your accounting period didn't match the tax year, or one of the other full-page conditions applies.
Do I need SA103 if I earned less than £1,000?
Receipts up to £1,000 are covered by the trading allowance and don't need to be reported, unless they're from a connected party. You may still choose to file to pay voluntary Class 2 NICs or support a Maternity Allowance claim.
Can I claim the trading allowance and expenses?
No. If you claim the £1,000 trading allowance you can't deduct allowable expenses or claim other allowances.
Can I put total expenses in one box on SA103S?
Yes, if your annual turnover was below £90,000 you may put your total expenses in box 20.
What date goes in box 7 of SA103S?
The date your accounts were made up to. If that's 5 April 2026, enter 05 04 2026. A date before 31 March 2026, unless you stopped trading, or after 5 April 2026 means using the full pages.
