The SA103 is the Self-employment supplementary page to the SA100 tax return, completed once for each sole-trader business. It comes in two versions: the short SA103S for straightforward businesses with turnover under the VAT threshold, and the full SA103F for larger businesses or those that need the detailed breakdown.
Who completes it
Anyone who ran a business as a sole trader or was otherwise self-employed in the tax year, with one page for each business. The trading allowance means a business with gross income of £1,000 or less need not be reported at all.
The SA103S (short) can be used when annual turnover was below the VAT registration threshold of £90,000 and nothing complicated applies. The SA103F (full) is needed when turnover was £90,000 or more, the accounting date changed, there are brought-forward or carried-back losses to deal with, or any of the other situations the SA103S notes rule out. Lloyd’s underwriters use the SA103L.
What it asks for
- Business details: the description of the business, its start or cessation date if it started or ceased in the year, the accounting period and whether the cash basis is used (it is the default for the self-employed since 2024-25).
- Income and expenses: turnover and other income, then expenses either as one total or broken down by type, with the disallowable amounts shown separately on the full page.
- Tax adjustments: capital allowances, including the Annual Investment Allowance, balancing charges, goods taken for own use, transition profits from basis period reform (spread over the five years to 2027-28), losses and the final taxable profit.
- National Insurance: the Class 4 exemption tick and the voluntary Class 2 choice. Class 4 for 2025-26 is 6% of profits between £12,570 and £50,270 and 2% above that.
In Tax Optimiser
Add the Self-employment section, choose short or full pages and add one business card per trade. Where a total box is the sum of the boxes above it the screen shows what they add up to, with a Use this link to fill it in. The taxable profit flows into the calculation together with Class 4 and Class 2 National Insurance. The SA103L page is not offered.
Read more: entering income on a Self Assessment return.
