Quick answer: You must register for Self Assessment if your self-employed income exceeds £1,000 in a tax year, or if you earn over £100,000, have untaxed income, or need to claim certain reliefs. The deadline to register for 2025/26 is 5 October 2026. Late registration incurs penalties.
Registration threshold
You must register for Self Assessment if your total self-employed income (including gig work) exceeds £1,000 in a tax year. This is known as the trading allowance. Below £1,000 you do not need to file, but you also cannot claim expenses.
If you earn over £1,000 and do not register, HMRC can issue penalties. The penalty for late registration is a percentage of unpaid tax, increasing over time.
How to register
You must register by 5 October following the end of the tax year in which you started self-employment. For 2025/26 (which ends 5 April 2026), the registration deadline is 5 October 2026.
Register online at gov.uk — search "register self assessment HMRC". You will receive a Unique Taxpayer Reference (UTR) by post within 10 working days. Keep this number — you need it to file your return.
After registration
Once registered, file your Self Assessment online by 31 January following the end of the tax year. Pay any tax owed by the same deadline. For 2025/26 earnings, file and pay by 31 January 2027. Missing this deadline incurs an automatic £100 penalty.
Estimates based on HMRC 2025/26 rates. General guidance only — not financial, tax, or legal advice.
Your actual liability may differ. Consult a qualified accountant for personalised advice. Verify rates at gov.uk.