Self Assessment

Self Assessment is HMRC's system for reporting and paying tax on income that hasn't already been taxed at source. Sole traders, freelancers, landlords, partnership members, and most Ltd company directors need to file one each year.

Two deadlines matter. Paper returns are due 31 October after the tax year ends. Online returns — and the tax payment — are due 31 January. For 2024-25, that means filing and paying by 31 January 2026.

You also need to register with HMRC if you've never filed before: the deadline is 5 October after your first self-employed tax year. Registration gives you a Unique Taxpayer Reference (UTR) — you'll need it forever after.

Penalties are automatic and escalate fast: £100 the moment you're a day late, additional daily penalties after three months, and percentage-based penalties on unpaid tax from 30 days late. File and pay on time even if you can't pay everything — HMRC offers a Time to Pay arrangement for the balance.

Related terms

• Payments on account — HMRC advance tax payments — half your prior-year bill, due 31 January and 31 July.
• Class 4 National Insurance — NI for sole traders — 6% main rate on profits between £12,570 and £50,270, 2% above.
• Personal Allowance — The first slice of income you can earn tax-free each year — £12,570, frozen until April 2031.
• Tax code — The code HMRC gives your employer so they know how much of your pay is tax-free under PAYE.
• Trading Allowance — A £1,000 tax-free allowance for casual self-employment income — no need to register with HMRC below this.
• UTR (Unique Taxpayer Reference) — The 10-digit number HMRC assigns you for Self Assessment — you need it for every return, payment, and HMRC conversation.