The short answer: for the 2025 to 2026 tax year, register with HMRC by 5 October 2026 if you are new to Self Assessment, file a paper return by 31 October 2026 or an online return by 31 January 2027, and pay any tax due by 31 January 2027. Missing a deadline brings automatic penalties, so it pays to plan ahead.
Key dates for the 2025 to 2026 tax year
- 5 October 2026: deadline to tell HMRC you need to complete a return, if you have not sent one before or did not need to for 2024 to 2025
- 31 October 2026: deadline for a paper tax return
- 30 December 2026: file online by this date if you want HMRC to collect tax you owe through your tax code
- 31 January 2027: deadline for your online tax return, and for paying the tax you owe
- 31 July: the second payment on account deadline, for people who pay their tax in instalments
Filing online gives you three more months than a paper return, which is why most people do it that way.
Penalties for filing late
- An initial £100 penalty as soon as the deadline passes
- After 3 months, additional daily penalties of £10 a 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, whichever is greater
Penalties for paying late
If you pay your tax bill late, you get penalties of 5% of the tax unpaid at 30 days, 6 months and 12 months, and you are also charged interest on the amount owed.
How to avoid penalties
- Gather your records early, well before the deadline (see our checklist).
- File early. You can file as soon as the tax year ends on 5 April.
- Set money aside during the year for your tax bill.
- Put the dates in your diary, or ask us to remind you.
- If you think you will miss a deadline, talk to us straight away.
Making Tax Digital is changing things for some people
If you are a sole trader or landlord with income over the government thresholds, Making Tax Digital for Income Tax will add quarterly updates. See our guide.
Sources: gov.uk, Self Assessment tax return deadlines and penalties, checked 25 September 2026.
Common questions
Is 31 October a firm deadline?
It is the deadline for paper returns. If you file online, your deadline is 31 January. Most people file online.
What if I did not know I needed to register?
Register as soon as you realise, and speak to us. Acting quickly gives you the best chance of limiting any penalties.
Can I pay my tax in instalments?
Some people make payments on account, with the second one due by 31 July. If you cannot pay in full, contact HMRC or ask us about your options as early as you can.
General information only, not personal advice. Tax rules, rates and thresholds change, so check gov.uk or speak to us about your own situation.