Key takeaways

  • Register by 5 October after the end of the tax year in which you first need to file, for example by 5 October 2026 for income in 2025/26.
  • Self-employed people register for Self Assessment and National Insurance in one online application.
  • HMRC sends a 10-digit Unique Taxpayer Reference (UTR), usually within 15 days, or longer if you are abroad.
  • Registering late is not a penalty in itself, but a failure to notify penalty can apply if tax is still unpaid at 31 January.
  • If you are already registered but did not file last year, you may need to reactivate your account rather than register again.

Before you can file a Self Assessment tax return, HMRC needs to know you exist as a taxpayer with income outside PAYE. Registering gives you a Unique Taxpayer Reference (UTR) and sets up your Self Assessment account. It takes about 15 minutes online, but you need to do it in good time.

Do you need to register?

You need to file a return, and so register, if in the tax year you:

  • were self-employed as a sole trader with income over £1,000 before expenses
  • were a partner in a business partnership
  • had Capital Gains Tax to pay (other than UK property gains reported only through a 60-day return)
  • had to pay the High Income Child Benefit Charge and are not paying it through PAYE
  • had untaxed income, such as rental income, tips, savings interest or dividends over the reporting limits, or foreign income
  • received a notice from HMRC asking you to file

HMRC’s online checker tells you if you need to file. See who needs to file for the detailed rules.

The deadline: 5 October

You must tell HMRC by 5 October after the end of the tax year in which you first had the income. For the 2025/26 tax year (which ended on 5 April 2026), the deadline was 5 October 2026. For 2026/27 it is 5 October 2027.

If you register after 5 October, you still need to file and pay by 31 January. If any tax is unpaid at 31 January, HMRC can charge a failure to notify penalty based on the unpaid amount.

How to register

The route depends on why you need to file.

If you are self-employed

Register online as a sole trader. One application registers you for Self Assessment and for Class 2 and Class 4 National Insurance. You need:

  • your name, address, date of birth and National Insurance number
  • your phone number and email
  • the date you started self-employment
  • the type of business and its address

You will set up a Government Gateway or GOV.UK One Login account as part of the process. See also how to register as a sole trader.

If you are not self-employed

Use the online form for people who need to file but are not self-employed, for example landlords, people with investment income or those paying the Child Benefit charge. Paper form SA1 is available if you cannot apply online.

If you are a partner

Each partner registers individually (form SA401 if not online), and the nominated partner registers the partnership (form SA400) so it can file a partnership return.

If you have filed before

If you have a UTR from an earlier year but did not need to file last year, you may need to reactivate your Self Assessment record rather than register again. Use the same online service and give your UTR, or contact HMRC.

What happens next

  1. HMRC sends your UTR by post, normally within 15 days (21 days if you are abroad). It also appears in your HMRC online account and app.
  2. You receive an activation code for online Self Assessment, if you set up a new account; activate it within 28 days.
  3. HMRC sends a notice to file a return for the tax year concerned.

Keep your UTR safe: you need it to file, to pay and for your accountant to act for you.

After registering

  • Keep records of income and expenses from the start; see record keeping for Self Assessment.
  • Check whether Making Tax Digital applies. If your gross self-employment and property income is over £50,000 (from April 2026), £30,000 (from April 2027) or £20,000 (from April 2028), you must use MTD for Income Tax; see the MTD timeline.
  • Plan for payments on account, which start once your bill is £1,000 or more.
  • Diary the deadlines: see Self Assessment deadlines.

Stopping Self Assessment

If you no longer need to file, for example because you stopped self-employment, tell HMRC. Until HMRC withdraws the notice to file, you must keep filing, or you will receive late filing penalties.

Frequently asked questions

What is the deadline to register for Self Assessment?

5 October after the end of the tax year in which you first need to file.

How long does it take to get a UTR?

Usually within 15 days of registering, or 21 days if you are abroad.

Do I need to register if I earn less than £1,000 from self-employment?

Not usually. Gross self-employment income of £1,000 or less is covered by the trading allowance, unless you need to file for another reason.

Can I register for Self Assessment online?

Yes. Most people register online through GOV.UK, using a Government Gateway or GOV.UK One Login account.

Sources

Rates, thresholds and rules in this guide were checked against HMRC and GOV.UK guidance in October 2026. Tax rules change, so check the current position on GOV.UK or with a qualified adviser before acting. This guide is general information, not personal advice.