The Self Assessment Timeline: From Registration to Payment

The timeline at a glance

The dates below are for filing a return for the 2025/26 tax year (6 April 2025 to 5 April 2026), which is the return most people are working on during 2026 and early 2027.

Step 1: Register by 5 October

You must tell HMRC by 5 October after the end of the tax year if you need to complete a return and you either haven't filed before, or you registered before but sent no return for the previous year. You register online on GOV.UK: as a sole trader if you're self-employed, or as an individual otherwise. Registering sets up your Class 2 and Class 4 National Insurance if you're self-employed.

Register after 5 October 2026 and HMRC will give you a new filing deadline, three months from the date of their letter or email. The payment deadline doesn't move: tax is still due by 31 January 2027, and a 'failure to notify' penalty is possible if tax is left unpaid.

How to complete a Self Assessment tax return, step by step

Step 2: Your UTR and activation code

After registering, HMRC posts your 10-digit Unique Taxpayer Reference (UTR). If you're new to the online service, an activation code follows by post too. These arrive by post, so allow a few weeks and register well before 5 October; leaving it to the deadline is one of the most common ways people end up filing late.

Once your account is activated, you sign in with your Government Gateway ID for everything that follows: filing the return, checking the calculation and paying. If your UTR hasn't arrived, GOV.UK has a page for checking when to expect a reply.

Step 3: File the return

You can send the return any time from 6 April after the tax year ends. Paper returns must reach HMRC by 11:59pm on 31 October; online returns by 11:59pm on 31 January. Submitting online gives you around three extra months and confirms receipt immediately.

If you owe less than £3,000 and want it collected through your PAYE code instead of paying a lump sum, the online return must be in by 30 December.

Use the Self Assessment Calculator to see what you would save

Step 4: Pay by 31 January

HMRC must receive the payment, not just the return, by 11:59pm on 31 January. If payments on account apply, half the following year's bill is also due that day and the second half on 31 July. Payments on account aren't needed when the bill is under £1,000 or when more than 80% of your tax was already collected at source through PAYE.

Interest runs on anything paid late, so paying a few days before the deadline beats paying a few days after.

Self Assessment explained: who files and what's on the return

If you miss a deadline

Late filing and late payment each carry their own penalties, and both apply even if no tax is due.

Paying late is charged separately

Paying late adds 5% of the tax unpaid at 30 days, another 5% at six months and a further 5% at twelve months, plus interest. If you had a reasonable excuse, you can appeal the penalty online on GOV.UK, usually within 30 days of the notice.

Step 5: Keep your records

Keep records supporting the return for at least 22 months after the end of the tax year if you file online, and for longer if you're self-employed, in case HMRC asks questions or you need to amend. Online returns can be amended up to 12 months after the 31 January deadline.