Register for Self Assessment

You register for Self Assessment when you first need to send HMRC a tax return. Registering gives you a Unique Taxpayer Reference (UTR), a 10-digit number that you need to file the return.

Who needs to register

You need to register if, in the tax year (6 April to 5 April), any of these applied:

• you were self-employed as a sole trader and earned more than £1,000 before deducting anything you can claim tax relief on
• you were a partner in a business partnership
• you had to pay Capital Gains Tax, for example on selling a second property or shares
• you had to pay the High Income Child Benefit Charge and do not pay it through PAYE
• you had untaxed income, such as rent from property or land, tips and commission, savings interest, dividends or foreign income

You can also register by choice. A tax return is accepted as proof that you are self-employed, for example when you claim Tax-Free Childcare or Maternity Allowance, and some people file to pay voluntary National Insurance.

When to register

You must tell HMRC by 5 October after the end of the tax year in which you first needed to send a return. If you started working for yourself in August 2026, which falls in the 2026 to 2027 tax year, you register by 5 October 2027. The same deadline applies if you registered before but did not need to send a return for the previous tax year.

If you tell HMRC after 5 October, you could get a failure to notify penalty. It is a percentage of the tax still unpaid after 31 January, so it falls on you only if you also pay late.

How to register

Registering online is quickest. You sign in to your HMRC online account, or create one if you do not have one. You may need to prove your identity with photo ID such as a passport or driving licence. You can save your progress and finish later. You cannot register online if you do not live in the UK.

To register by post, fill in, print and post the form that fits your situation:

• form CWF1 if you are self-employed as a sole trader
• form SA1 if you need to file for another reason, such as Capital Gains Tax or income from a trust
• form SA401 if you are a partner in a partnership, which also registers you for Class 2 National Insurance

The nominated partner must also register the partnership itself. Limited liability partnerships and partners that are not individuals, such as companies and trusts, register in different ways.

If you registered before and your account has gone inactive, reactivate it instead of registering again. You can do this online, or by post with form CWF1 and your UTR. Filing without reactivating can delay your return.

Getting your UTR

If you need to set up an online account for Self Assessment, HMRC may post an activation code, usually within 7 working days. Sign in with the code to activate the account.

What to do next