Self-employment page (SA103)
This is a working walkthrough of what to enter in each Self Assessment section for a UK freelancer sole trader — not a general overview but the actual line-by-line guidance that gets you filed correctly. Uses 2024/25 tax-year references applicable to the 2025 SA return.
Self-employment page (SA103)
Turnover box: gross income before deducting anything.
Allowable expenses (either itemised across the categories on the form, or a single 'total expenses' box if under £85k turnover using the short-form SA103S).
Capital allowances: AIA on qualifying equipment.
Net profit: HMRC calculates automatically.
Business-use of home: either flat rate (£6/week = £312/year) or apportioned actual costs (rent/mortgage-interest, utilities, council tax proportion).
Motoring: simplified expenses (per-mile rate) or actual costs including capital allowances.
Adjustments, reliefs, pension, Gift Aid
Personal pension contributions: total amount you paid in the tax year. HMRC adds basic-rate relief automatically at your pension provider; higher-rate relief calculated here.
Gift Aid donations: total amount donated (excluding the 25% top-up).
Loss carry-back: if this year's business was loss-making and you're carrying back to a prior year.
Marriage Allowance transfer to spouse: tick the box.
Student loan status: plan number (1/2/4/5) — HMRC calculates repayment.
Check-and-submit gotchas
HMRC's calculation appears at the end. Common surprises: - Payments on account added automatically if bill > £1,000. - Class 4 NI added on top of income tax. - Higher-rate pension relief showing as reducing your bill. - Class 2 NI is now voluntary but if ticked adds to the bill.
Save the submission receipt PDF — you'll need it if HMRC queries anything.
Worked example
Zara: £34,000 turnover, £3,800 expenses (software, business insurance, phone-portion, travel). Home office: flat rate £312. Motoring: 1,200 business miles × 45p = £540. Total expenses: £4,652. Net profit: £29,348. Personal pension £2,000 contributed. Gift Aid £120. HMRC calculates: personal allowance £12,570; taxable £16,778 at 20% = £3,356; Class 4 NI (£29,348 - £12,570) × 6% = £1,007. Total: £4,363 tax + NI, less any tax already paid on other income.
Reference table
| Section | Line | Note |
|---|---|---|
| Self-employment (short) | Business income | Gross turnover |
| Self-employment (short) | Allowable expenses | Business use only |
| Self-employment (short) | Net profit | Auto-calculated |
| Reliefs | Pension contributions | Total paid, HMRC adds relief |
| Reliefs | Gift Aid | Amount donated |
| Underpaid tax | From PAYE code | If you had employment |
Section-by-section prep checklist
- Annual P&L from accounting software (or manual reconciliation)
- Bank statements for full tax year
- Home office calculation (flat rate or apportioned)
- Mileage log with business miles counted
- Pension contribution statements
- Gift Aid records
- Any P60/P45 from employment during the year
- Untaxed interest and dividend statements
- Previous year's SA to reference structure
SA103S if turnover under £85k. SA103F if over. Most freelancers use the short version.
You report a loss. HMRC lets you carry back to a prior year, offset against other income the same year, or carry forward. Choose the option best for your circumstances.
Yes — AIA gives 100% first-year deduction on qualifying equipment. Enter under capital allowances in the self-employment section.
Not to file, but to defend claims if HMRC enquires. Keep for at least 5 years after the 31 January filing deadline.
HMRC accepts rounded pounds. Round down to your favour on income (e.g. £34,000.65 → £34,000); round up on expenses (£4,321.10 → £4,322). The rounding rule doesn't change the tax bill materially but simplifies entry.
Sources & official references
Related on FreelanceToolkit UK
Related: UK Tax Rates Reference 2025/26 — from FreelanceToolkit UK.
Related: UK VAT Rates Reference — from FreelanceToolkit UK.
Related: UK VAT Registration Checklist 2025/26 — from FreelanceToolkit UK.
Related: Tembo vs Habito UK 2026 — Freelancer Mortgage Brokers Compared — from FreelanceToolkit UK.
This guide is general information based on UK rules for the 2025/26 tax year. It is not personal tax or legal advice. For decisions affecting your tax position or legal exposure, consult a qualified accountant or solicitor.