Before you start filing
Filing Self Assessment online through the HMRC portal is the standard route for UK freelancers — paper returns are largely deprecated (deadline 31 October vs 31 January online) and third-party software is optional. This walkthrough covers exactly what you'll see on screen when you file, in the order HMRC presents it, plus the sections most freelancers skip incorrectly.
Before you start filing
Have to hand: your UTR, Government Gateway login, P60/P45 from any employment, records of self-employment income and expenses, records of dividends/interest/other income, pension contribution certificates, Gift Aid records, student loan status.
Gather these before you log in — the HMRC session logs you out after inactivity and losing your progress mid-return is a common source of missed deductions.
The sections you'll walk through
Tell us about you — personal details, marital status, marriage allowance.
Tailor your return — HMRC asks which pages apply (self-employment, employment, foreign income, capital gains, etc.). Tick every applicable box; missing one means you can't add data later without restarting the tailored questions.
Self-employment page — turnover, allowable expenses, capital allowances, net profit.
Employment page (if applicable) — from P60/P45.
Other income — interest, dividends, foreign income, rental.
Adjustments and reliefs — pension contributions, Gift Aid, marriage allowance transfer, student loan.
Check and submit — HMRC shows the tax owed. You can save and return; submission generates a submission receipt.
Sections freelancers commonly miss
Pension contributions with higher-rate relief. Personal pension contributions attract basic-rate relief automatically but higher-rate relief must be claimed on the return. Missed by many first-time filers.
Marriage Allowance transfer — £252 transferable to a spouse if one earns under the personal allowance.
Gift Aid higher-rate relief.
Student loan repayments — if applicable, HMRC won't calculate them without ticking the box.
Class 2 NI voluntary contributions — now voluntary if profits below £6,725; still worth paying for state pension entitlement.
Worked example
Priya's 2024/25 tax year: £48,000 self-employment turnover, £4,200 allowable expenses, £3,500 higher-rate pension contribution, £500 Gift Aid. Filing steps: (1) sign in with Government Gateway, (2) tailor the return to include self-employment + pension + Gift Aid pages, (3) enter £48,000 turnover and £4,200 expenses → net profit £43,800, (4) enter pension £3,500 in adjustments, (5) enter Gift Aid £500. HMRC calculates: personal allowance £12,570; taxable £31,230 at 20% = £6,246; Class 4 NI £1,873; higher-rate pension top-up nil (she's basic-rate); Gift Aid basic-rate top-up nil (auto). Bill: £8,119. Payments on account for 2025/26 apply since > £1,000.
Reference table
| Section | Time needed | Common freelance oversight |
|---|---|---|
| Tell us about you | 3 min | Marriage allowance not ticked |
| Tailor your return | 5 min | Missing self-employment page tick |
| Self-employment | 15-30 min | Personal-use expenses claimed 100% |
| Other income | 5 min | Untaxed interest missed |
| Adjustments & reliefs | 10 min | Higher-rate pension relief not claimed |
| Check and submit | 5 min | Not printing/saving the submission receipt |
Before-you-file checklist
- UTR, Government Gateway login, tax year P60s
- 12-month P&L exported from accounting software
- Pension contribution certificates for the tax year
- Bank interest statements (for untaxed interest)
- Dividend vouchers (for any received)
- Gift Aid donation records
- Student loan plan number (if applicable)
- Home office allowance calculation (flat rate or apportioned)
- Mileage log if claiming
Yes — HMRC saves progress every few minutes. Sessions time out after ~20 minutes of inactivity but data persists. Log back in and continue.
No — HMRC's portal accepts direct entry. Software (FreeAgent, QuickBooks, Xero) makes the number-generation faster but isn't required for a straightforward return.
Technically yes, deadline 31 October — three months earlier than the online 31 January deadline. Almost no reason to file paper today.
You can amend within 12 months of the original filing deadline. Sign back in → view submitted return → make amendment.
Yes, until you formally deregister. HMRC expects a return even if income was nil that year.
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.