Answers · UK 2025/26
When do you need to register for Self Assessment?
You must register for Self Assessment by 5 October following the tax year in which you first need to file. For 2025/26 income, register by 5 October 2026.
Full answer
HMRC requires you to register for Self Assessment if you are self-employed (sole trader or partner) with gross income over £1,000; a company director; have untaxed income such as rental income over £1,000, savings interest over £10,000, or dividends above £500; have capital gains; earn over £100,000; or claim certain reliefs. The deadline to register for the 2025/26 tax year is 5 October 2026. Failing to register on time can result in a £100 penalty, even if no tax is owed. You register online via the HMRC website (or by post using form SA1 for non-self-employed taxpayers). Once registered, you will receive a Unique Taxpayer Reference (UTR) number. Self-employed individuals also need to register with the Class 2 and Class 4 NI system at the same time.
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This answer is informational only and does not constitute financial, tax or legal advice. Figures are for the 2025/26 UK tax year. See our methodology and sources.