Register for Self Assessment by 5 October 2026: what you need to know

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If you had untaxed income in the 2025/26 tax year (6 April 2025 to 5 April 2026) and have never filed a Self Assessment return, you must tell HMRC by Monday 5 October 2026. You do this by registering for Self Assessment. Registering late can lead to a penalty.

Who needs to register by 5 October 2026?

You will usually need to register if, in the 2025/26 tax year, you:

Were self-employed and earned more than £1,000 in gross income (before expenses)
Started renting out property and your income went above the property allowance
Were a partner in a business partnership
Owed Capital Gains Tax, for example after selling a second property or shares
Had other untaxed income that isn't collected through PAYE

If you already filed a return last year, you don't need to register again. If you filed last year but no longer need to, tell HMRC. Until they confirm, you should keep meeting your filing obligations.

Not sure where you stand? HMRC has a free online checker on GOV.UK.

How do you register for Self Assessment in 2026?

HMRC launched an improved online registration service this month. It works through your Personal Tax Account, which you can set up with a Government Gateway or GOV.UK One Login.

The main changes are:

Some of your details are pre-filled.
You can save your progress and come back later.
You get an email or text when registration is complete.
Your Unique Taxpayer Reference (UTR) should appear in your online account within 72 hours. Before, it could take up to 15 days by post.

The UTR is a 10-digit number you need before you can file. Our guide explains what a UTR number is.

What happens if you miss the 5 October deadline?

You can still register late, but HMRC may charge a "failure to notify" penalty. It is not a fixed fine. It is a percentage of any tax left unpaid because you didn't tell HMRC in time. The rate depends on whether the delay was deliberate and whether you came forward yourself. Late filing and late payment penalties can also apply on top.

Key dates for the 2025/26 tax return

Date	What's due
5 October 2026	Register for Self Assessment (first-timers)
31 October 2026	Paper return deadline
30 December 2026	Deadline to have small tax bills collected through your PAYE tax code
31 January 2027	Online return deadline and payment of tax owed
31 July 2027	Second payment on account

Your first bill on 31 January can include payments on account towards the following year's tax. Budget for it early.

Does Making Tax Digital change anything?

Making Tax Digital for Income Tax began on 6 April 2026 for self-employed people and landlords with qualifying income over £50,000. They must keep digital records and report through compatible software. The threshold is due to fall in later years. Registering for Self Assessment is still the first step, and we can help you work out whether MTD applies to you.

Read our guide to Making Tax Digital for Income Tax.

Frequently asked questions

When is the Self Assessment registration deadline for 2026?5 October 2026, for the 2025/26 tax year.

Do I need to register if I earned under £1,000 self-employed?Generally not, because of the trading allowance. Check HMRC's online tool if you have other income too.

How long does it take to get a UTR?Under HMRC's new online service it should appear in your account within 72 hours. Other routes can take longer, so don't leave it to the last minute.

Can an accountant register for me?

Yes. Agents still use HMRC's existing registration routes rather than the new individual service.

Need help with Self Assessment?

At Styles & Associates we register you with HMRC, prepare your return, calculate what you owe or are owed, and file it for you. Call 01420 541 554 for a free quote, or get in touch here.