SA103S or SA103F for self-employment

Which pages to use

The SA103S notes for 2025 to 2026 say to fill in the short pages if turnover was less than £90,000, or would have been for a full year of trading. GOV.UK's SA103S publication page describes the short form as being for relatively simple tax affairs with annual turnover below the VAT threshold for the tax year.

The SA103F notes for 2025 to 2026 say to use the full pages if any of these apply:

• Turnover was £90,000 or more, or would have been for a full year of trading (SA103F notes).
• The profits or losses of the accounting period need adjusting because it ended before 31 March 2026, was not 12 months long, or did not end in the tax year.
• There is adjustment income from changing accounting basis.
• Profits chargeable to Class 4 National Insurance need adjusting.
• The client was in HMRC's Managing Serious Defaulters programme during the year.

If none of these apply, the SA103F notes direct the client to the short pages. A client below £90,000 can still need the full pages, for example a sole trader with a 30 June year end, because their profit must be apportioned to the tax year.

The short and full pages compared

What the full pages add

Business details include the accounting period and, where needed, the adjustment in box 68 for a period that ended before 31 March 2026 or was not 12 months long. The SA103F notes say the client may need to add together or apportion accounting periods to work out the profit for the tax year. Transition profit does not go in box 68. See basis period reform.

Capital allowances are broken down by type: the Annual Investment Allowance in box 49, writing down allowances at 18% and 6% in boxes 50 and 51, zero-emission car allowance in box 52.1, the Structures and Buildings Allowance in box 53, electric charge-points in box 54, and 100% and other enhanced allowances in box 55. The 2025 to 2026 notes say box 55 includes the 40% first-year allowance for qualifying plant or machinery bought on or after 1 January 2026. Balancing charges go in box 59. See capital allowances rates for 2026.

Adjustments to profit include goods taken for own use in box 60, the adjustment for a change of accounting practice in box 71 and the averaging adjustment for farmers, market gardeners and creators of literary or artistic works in box 72.

Losses

• Both sets of pages take the same three loss claims, in boxes 33 to 35 on the SA103S and boxes 78 to 80 on the SA103F.
• Loss for the year set against other income of the same year. The SA103F notes say relief against total income is limited to the greater of £50,000 or 25% of adjusted income.
• Loss carried back, including terminal loss relief for a business that ceased in 2025 to 2026, with details of each year in the any other information box.
• Total loss carried forward against future profits of the same business.

Class 4 National Insurance

Both forms have a box for a client who is exempt from Class 4 contributions: box 37 on the SA103S and box 101 on the SA103F. For 2025 to 2026 the SA103F notes list those who reached State Pension age on or before 6 April 2025, were under 16 on 6 April 2025, or were not resident in the UK for tax purposes in the tax year. Only the full pages have box 102, which takes adjustments that reduce the profits chargeable to Class 4, such as losses brought forward that have not been set against Class 4 profits.

Questions