Self Assessment for sole traders: filling in the self-employment pages
Updated 11 October 2026 · 2026/27 tax year
If you file your own tax return, the self-employment pages (SA103) are where your business figures go. They're less scary than they look once your books are in order.
Short or full pages?
If your turnover was under £90,000 and your affairs are simple, you can usually use the short pages (SA103S). Otherwise, the full pages (SA103F). Filing online, HMRC asks questions and picks for you.
What goes in
- Turnover: everything you were paid for your work in the tax year
- Allowable expenses, split into HMRC's lines: materials, van and travel, wages, rent and insurance, repairs, phone and office, advertising, interest, bank charges, bad debts, accountant fees and other costs
- Your net profit (turnover less expenses)
- Any CIS taken off by contractors, which counts as tax already paid
Mileage and working from home
If you claim 45p a mile, it goes in with your van and travel costs. HMRC's flat rate for working from home goes with rent, rates and power.
Small costs?
If your costs are under £1,000, you could claim the £1,000 trading allowance instead of your actual costs.
Deadlines
- Paper return: 31 October after the tax year
- Online return: 31 January after the tax year
- Tax to pay: 31 January, plus any payment on account, and another on 31 July
This guide is general information, not tax advice. Check HMRC's guidance or ask an accountant about your own situation.