UK tax and accounts basics, explained

Self Assessment Tax Return Deadlines Explained

8 November 2026

General information, not tax adviceEvery figure here is quoted from GOV.UK, with the tax year it applies to. Your own position can differ, so check your HMRC online account and the linked GOV.UK page, or speak to a qualified accountant.

Self Assessment tax return deadlines are easy to miss if you only think about them once a year. This guide sets out each deadline for the 2025 to 2026 tax year as GOV.UK states it, with a link to the GOV.UK page behind every date. It's general information, not tax advice.

Key Takeaways

• The 2025 to 2026 tax year started on 6 April 2025 and ended on 5 April 2026.

• Online returns for that year are due by 11:59pm on 31 January 2027, and so is the tax you owe.

• To pay through your tax code, GOV.UK says to submit online by 11:59pm on 30 December 2026.

• If you register after 5 October 2026, HMRC will give you a different filing deadline, but the payment deadline stays 31 January 2027.

• A late return gets an initial £100 penalty, with more penalties after 3, 6 and 12 months.

What Self Assessment is

GOV.UK's overview of Self Assessment tax returns describes it as the system HMRC uses to collect Income Tax. Tax is usually taken automatically from wages and pensions, but people and businesses with other income must report it in a Self Assessment tax return.

You fill in the return after the end of the tax year it applies to. The tax year runs from 6 April to 5 April. HMRC works out what you owe from what you report.

Who has to send a return

GOV.UK's page on who must send a tax return says you must send one if, in the last tax year, any of these applied:

• you were self-employed as a sole trader and earned more than £1,000, before taking off anything you can claim tax relief on

• you were a partner in a business partnership

• you had to pay Capital Gains Tax when you sold or disposed of something that increased in value

• you had to pay the High Income Child Benefit Charge and don't pay it through PAYE

• you were an off-payroll worker repaying a student or postgraduate loan

You must also send a return if HMRC asks you to. If you're starting out on your own, our guide on how to register as self-employed in the UK explains the first steps.

The deadlines for the 2025 to 2026 tax year

The GOV.UK page on Self Assessment deadlines says the last tax year started on 6 April 2025 and ended on 5 April 2026. HMRC must receive your tax return and any money you owe by the deadline.

Registering after 5 October 2026

If you register after 5 October 2026, GOV.UK says HMRC will send you a letter or email with a different deadline for your tax return. It will be 3 months from the date on that letter or email. You must still pay the tax you owe by 11:59pm on 31 January 2027, or you'll get a penalty.

Paper or online

GOV.UK says the paper deadline comes before the online one. For 2025 to 2026, the paper deadline of 31 October 2026 has now passed. The online deadline is 31 January 2027. You can send a return any time on or after 6 April 2026, and GOV.UK points out that sending it earlier means you find out what you owe and have time to budget.

Payments on account and the 31 July date

Some people pay their tax in instalments called payments on account. GOV.UK's page on payments on account says each payment is usually half of the tax you owed the previous year, and they're due by midnight on 31 January and 31 July.

You don't have to make them if the tax you owed last year was less than £1,000, or if last year you paid more than 80% of the tax you owed outside Self Assessment, for example through your tax code. If your payments on account don't cover your bill, you pay the rest as a balancing payment by 31 January. Our guide to payments on account works through GOV.UK's examples.

What happens if you're late

The GOV.UK page on Self Assessment penalties lists the late filing penalties:

• an initial £100 penalty

• after 3 months, additional daily penalties of £10 per day, up to a maximum of £900

• after 6 months, a further penalty of 5% of the tax due or £300, whichever is greater

• after 12 months, another 5% or £300 charge, whichever is greater

If you pay late, GOV.UK says you'll get penalties of 5% of the tax unpaid at 30 days, 6 months and 12 months, and you'll also be charged interest on the amount owed. If you have a reasonable excuse, you can appeal against a penalty.

If you need to change your return

GOV.UK's page on changing your return says you can correct a tax return within 12 months of the Self Assessment deadline, online or by sending another paper return. If you file online, you must wait 3 days (72 hours) after filing before you update it.

Keeping your records

You'll need records, such as bank statements or receipts, to fill in your return correctly. Our guide to allowable expenses for the self-employed covers the costs GOV.UK says you can claim, and why you should keep proof of them.

Making Tax Digital is changing things for some people

From 6 April 2026, some sole traders and landlords have to keep digital records and send quarterly updates. Our guide to Making Tax Digital for Income Tax explains who it applies to and when.

For every date on one page, see our summary of key tax dates and thresholds.

Frequently asked questions

When is the Self Assessment deadline for the 2025 to 2026 tax year?

GOV.UK says you must submit your online tax return, and pay the tax you owe, by 11:59pm on 31 January 2027. Paper returns had to reach HMRC by 11:59pm on 31 October 2026.

What is the penalty for a late Self Assessment tax return?

GOV.UK says there's an initial £100 penalty. After 3 months there are daily penalties of £10 a day, up to £900, and there are further penalties after 6 and 12 months.

Can I send my tax return early?

Yes. GOV.UK says you can submit your return any time on or after 6 April 2026 for the 2025 to 2026 tax year. Sending it earlier means you find out what you owe sooner.

What if I register for Self Assessment after 5 October?

GOV.UK says HMRC will give you a deadline 3 months from the date of its letter or email. You must still pay the tax you owe by 31 January 2027.

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