SA103S boxes explained: where each figure goes
The SA103S is the short self-employment page most sole traders use. Its boxes are logical once you see the pattern — and getting them right matters, because a wrong box number is one of the most common (and avoidable) Self Assessment errors.
The shape of the form
SA103S runs in a simple order: your business details, then income, then expenses, then the profit or loss that falls out of the two. The numbered boxes that carry your money figures are the ones to know:
| Box | What goes in it |
|---|---|
| 9 | Turnover — your total takings / sales / fees |
| 10 | Any other business income |
| 10.1 | Trading income allowance (if you claim the £1,000 allowance instead of expenses) |
| 11–19 | Your expense categories (see below) |
| 20 | Total allowable expenses (boxes 11–19 added up) |
| 21 | Net profit |
| 22 | Net loss (if your expenses exceed your income) |
The expense boxes, 11 to 19
The nine expense boxes on the short form are grouped by type. The exact categories are:
| Box | Category |
|---|---|
| 11 | Cost of goods bought for resale or goods used |
| 12 | Car, van and travel expenses |
| 13 | Wages, salaries and other staff costs |
| 14 | Rent, rates, power and insurance costs |
| 15 | Repairs and maintenance of property and equipment |
| 16 | Accountancy, legal and other professional fees |
| 17 | Interest and bank and credit-card financial charges |
| 18 | Phone, fax, stationery and other office costs |
| 19 | Other allowable business expenses |
Postage and packaging you pay to send orders to customers go in Box 18 (phone, fax, stationery and other office costs) — not Box 11 (cost of goods). HMRC's own helpsheet lists 'postage' under office costs. Selling and final-value fees go in Box 19; payment-processing fees go in Box 17.
The £90,000 short-cut
If your turnover is below £90,000 (the VAT-registration threshold), you are allowed to use a 'three-line account': instead of splitting costs across boxes 11–19, you can put a single total in box 20. Keeping costs categorised anyway makes your year-end easier — but the option is there if you want simplicity.
Two neighbours: SA103F and SA105
- SA103F is the *full* self-employment page, used above £90,000 or when you need the detail. It has the same idea but more boxes, including a separate 'disallowable' column for the part of a cost you cannot claim. (A couple of its box numbers — 11 and 12 — are not in use, which surprises people.)
- SA105 is the *UK property* page for landlords. Its total rents go in box 20, and — importantly — residential mortgage interest is not an ordinary expense: it goes in box 44 and gives a basic-rate tax reduction instead.
This product line exists because a Chartered Accountant's flagship template once shipped with the wrong SA103S box numbers. Every box in our cheat sheet was read directly off HMRC's current published forms rather than from memory.
Sources: HMRC forms SA103S, SA103F and SA105 and their notes, plus Helpsheet 222, on gov.uk. General information, not tax advice — the HMRC form is always the authority.
General information, not tax or financial advice. Always confirm your own position with HMRC or a qualified adviser. This article was last checked against published gov.uk guidance on 13 July 2026. Rules and figures can change — always confirm your own position with HMRC or a qualified adviser.