How to register for Self Assessment

Scope: This guide is for individuals who need to tell HMRC about a Self Assessment return for the tax year ended 5 April 2026. It covers the registration route and 5 October 2026 notification date, not agent registration or company returns.

The short answer

First check that you need a return. If you do, use HMRC’s Self Assessment registration service. For the 2025 to 2026 tax year, HMRC says you must tell it by 5 October 2026 if you have not filed before, or if you registered previously but did not need a return for 2024 to 2025.

If you already have a Self Assessment record, the service may tell you to reactivate it. Do not create a second registration simply because you skipped a filing year. Filing without reactivating an existing account can delay the return.

Before registering

Use HMRC’s official checker and collect the facts for 6 April 2025 to 5 April 2026. A filing requirement can arise from self-employment, partnership income, gains, the High Income Child Benefit Charge or untaxed sources such as property, dividends or foreign income.

If the checker says no return is needed but HMRC has already issued a notice to file, do not ignore the notice. Use HMRC’s process for saying that a return is no longer required.

Choose the correct route

You have not registered before

Use HMRC’s registration service to tell HMRC that a return is required. The service asks questions to identify the appropriate route rather than requiring every visitor to choose a technical form in advance.

You registered before but did not file last year

You may need to reactivate the existing Self Assessment account. HMRC says the registration service will explain how where reactivation is needed.

You already file every year

You normally do not register again. Sign in using the existing account and check that HMRC expects a return for the year.

You are an agent registering a client

The public registration service links to a separate agent route. This guide does not cover agent authorisation or registration responsibilities.

The 5 October 2026 date

The notification date applies to the tax year that began on 6 April 2025 and ended on 5 April 2026. The deadline is 5 October 2026 for the new or returning filers described above. HMRC says telling it after that date could lead to a penalty.

If you register after 5 October 2026, HMRC will send a letter or email giving a return deadline three months from the date of that message. Tax must still be paid by 11:59pm on 31 January 2027. Register as soon as possible and do not wait for a penalty before acting.

What happens after registration

Keep the confirmation and monitor the contact details supplied to HMRC. If you are waiting for a Unique Taxpayer Reference, HMRC provides a service to check when a response can be expected.

Registration is not the same as filing. You still need to:

• keep the records needed to complete an accurate return;
• prepare the figures and relevant supplementary information;
• submit the return by the applicable deadline; and
• pay the bill by the payment deadline.

HMRC says Self Assessment tax is generally due by 31 January. Filing earlier can show the amount due sooner and give more time to budget.

Example: returning after a year without a return

Sam registered for Self Assessment in an earlier year but HMRC did not require a return for 2024 to 2025. A new untaxed source means a return is needed for 2025 to 2026. Sam uses the registration service by 5 October 2026 and follows its reactivation route rather than opening a duplicate account.

The example explains the process only. Whether the new income actually requires a return must be checked using HMRC’s decision service.

Common mistakes

• Registering before checking whether a return is actually needed.
• Creating another account instead of reactivating the existing Self Assessment record.
• Treating registration as completion of the tax return.
• Waiting for a UTR before beginning to assemble income and expense records.
• Assuming a late registration removes the 31 January payment obligation.

What to do next

1. Check whether a return is needed.
2. Use HMRC’s registration service.
3. Save the registration confirmation and use HMRC’s reply checker if necessary.
4. Check the filing and payment dates.
5. Prepare records and estimate the bill rather than waiting until January.