Your business income goes on the self-employment pages of the Self Assessment return. Online, HMRC asks the questions on screen; on paper they are form SA103. Either way, the same few figures decide your bill, and getting them right matters more than the form.
Written and reviewed by James Whitfield · Last reviewed 19 October 2026 · Checked against 2026/27 HMRC rates · Editorial standards · Methodology
Use the short self-employment pages (SA103S) if your tax affairs are simple and your annual turnover was below the VAT threshold, currently £90,000.13 Use the full pages (SA103F) if turnover was above it or your affairs are more complex.2 You report turnover, then either your allowable expenses or the £1,000 trading allowance (not both), and any capital allowances. The result is your taxable profit, which Income Tax and Class 4 NI are worked out on. With turnover under £90,000 you can give expenses as a single total.
Related: Your first tax return · Allowable expenses · Self Assessment calculator
Employed too, or a company director? Get all 7 tax packs in the Tax Pack Library — £9.99
HMRC's forms say who each version is for.12 Most sole traders use the short pages. The full pages are for larger or more complicated businesses.
| Short pages (SA103S) | Turnover below £90,000, simple affairs |
| Full pages (SA103F) | Turnover above £90,000, or complex affairs |
| Expenses on the short pages under £90,000 | One total is enough |
| Paper return for 2026/27 | 31 October 2027 |
| Online return for 2026/27 | 31 January 2028 |
1. Turnover: everything the business earned in the year, before any costs. If you are VAT-registered, follow the instructions on whether to include VAT.
2. Allowable expenses: costs incurred wholly and exclusively for the business, such as stock and materials, travel, premises and use of home, phone and office costs, staff, insurance and accountancy.4 Keep a total for each category even if you enter only one figure.
3. Or the £1,000 trading allowance: instead of expenses, you can deduct a flat £1,000. You cannot use both.4
4. Capital allowances, if you use traditional accounting and bought equipment or a vehicle.
5. Any adjustments, such as private use of something you put through the business, which you add back.
Personal items stay off the pages entirely: your drawings, your own tax bill and private spending are not expenses.4
Lee is a gardener in England with no other income. In 2026/27 turnover is £38,000 and allowable expenses are £8,000 (fuel and van costs, tools, insurance, phone). Turnover is under £90,000, so Lee uses the short pages.
| Turnover | £38,000.00 |
| Allowable expenses (one total) | £8,000.00 |
| Taxable profit | £30,000.00 |
| Income Tax: 20% × (£30,000 − £12,570) | £3,486.00 |
| Class 4 NI: 6% × (£30,000 − £12,570) | £1,045.80 |
| 2026/27 bill | £4,531.80 |
Choose whichever deducts more. A side business with £3,200 of income and £400 of costs is better off with the allowance: taxable profit is £2,200 instead of £2,800. Someone with £8,000 of costs, like Lee, should claim the expenses.4
If you claim the allowance, you cannot also claim capital allowances.4
Entering profit as turnover, or turnover as profit. Turnover goes in first; profit is what the pages work out.
Claiming drawings, your own tax bill, commuting, fines or everyday clothing as expenses. None of these are allowable.
Claiming the trading allowance and expenses together for the same income.4
Leaving out a salary or other income elsewhere on the return. The self-employment pages are only one part; the bill depends on all your income.
Use the short pages (SA103S) if your turnover was below the VAT threshold, currently £90,000, and your affairs are simple. Use the full pages (SA103F) if turnover was above that or your affairs are more complex.
Yes, if your turnover was under £90,000 you can give a single total for allowable expenses. Keep the breakdown in your records in case HMRC asks.
On the self-employment pages, in place of your expenses. You deduct £1,000 from turnover instead of claiming actual costs, and you cannot claim both for the same income.
No. Drawings are not income or expenses. The self-employment pages ask only for turnover, allowable expenses or the trading allowance, capital allowances and adjustments.
31 October 2027 on paper or 31 January 2028 online. Any tax owed for 2026/27 is also due by 31 January 2028.
The rates, thresholds and rules in this guide are drawn from the official HMRC and GOV.UK sources below, using the confirmed 2026/27 figures. Each link opens the relevant official page in a new tab.
The sole trader tax calculator turns this guidance into a concrete monthly take-home and tax reserve estimate, based on 2026/27 HMRC rates. Enter taxable profit — not turnover.