The online Self Assessment tax return for the 2025-26 tax year, and any tax you owe, must reach HMRC by 11:59pm on 31 January 2027. That date is a Sunday, so it is sensible to treat Friday 29 January as your real deadline. This guide covers the key dates, the penalties for missing them and a simple checklist to get your return done early.
It is general information from public sources such as GOV.UK and the Low Incomes Tax Reform Group, not personal tax advice. If your finances are complicated, speak to a qualified accountant.
Key Self Assessment dates for 2025-26
| Date | What happens |
|---|---|
| 5 October 2026 | Deadline to register for Self Assessment if you are new (already passed) |
| 31 October 2026 | Paper return deadline (already passed) |
| 30 December 2026 | Deadline to ask for tax to be collected through your PAYE tax code, if you qualify |
| 31 January 2027 | Online return, tax owed for 2025-26 and first payment on account for 2026-27 |
| 31 July 2027 | Second payment on account |
The 2025-26 tax year ran from 6 April 2025 to 5 April 2026. You can send your return at any time after the tax year ends, so there is no need to wait until January.
Who usually needs to file
You may need a return if you are self-employed, a partner in a business, a landlord, or have other untaxed income above certain limits. Many people with only PAYE income do not. HMRC has a free online checker on GOV.UK that tells you whether you must file. If you have a trading side income, remember the 2026 changes to Making Tax Digital for Income Tax, which we explain in our MTD deadlines guide.
What to gather before you start
- Your Unique Taxpayer Reference (UTR) and Government Gateway login.
- Records of income: invoices, bank statements and, if relevant, rental income. Our guide to a professional invoice helps you keep them tidy.
- Business expenses and receipts.
- P60 or P45 forms and details of other income such as savings interest.
- Pension contributions and other reliefs you plan to claim.
Keep your records safe. HMRC can ask you to prove figures for several years after the deadline.
Penalties for missing the deadline
Filing and paying are separate duties, so you can be penalised for both. These figures come from GOV.UK.
| When | Late filing penalty | Late payment penalty |
|---|---|---|
| 1 day late | £100 (even if you owe no tax) | Interest starts |
| 30 days late | No new filing penalty | 5% of tax still unpaid |
| 3 months late | £10 a day for up to 90 days (maximum £900) | No new penalty |
| 6 months late | 5% of tax due or £300, whichever is greater | Another 5% of tax still unpaid |
| 12 months late | Another 5% or £300, whichever is greater | Another 5% of tax still unpaid |
Penalties must be paid within 30 days of the notice. If you have a reasonable excuse, you can appeal, usually within 30 days of the penalty notice. If you cannot pay in full, contact HMRC early about a payment plan. Interest is also charged on late tax.
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Payments on account explained
If your last Self Assessment bill was £1,000 or more, and less than 80% of your tax was collected at source, HMRC asks you to pay in advance towards next year. These payments on account are normally half of last year’s bill each, due on 31 January and 31 July. For example, if your last bill was £3,000, each instalment is usually £1,500. That means your 31 January 2027 payment can be larger than you expect, because it combines the balance for 2025-26 with the first instalment for 2026-27.
A simple plan to finish early
- Collect your records this week and tick off the list above.
- Log in to your Government Gateway account and start the return. You can save and come back.
- Submit by mid-January, so any login or identity problem can be fixed.
- Pay by Friday 29 January 2027 and allow for bank processing time.
- Keep your confirmation and a copy of your figures.
Watch for scam emails and texts claiming to be from HMRC around the deadline. Genuine messages do not need you to rush a payment through a link, so go to GOV.UK directly. Our guides on stopping spam calls and texts and spotting a fake website explain what to look for.
Frequently asked questions
Do I get a penalty if I owe no tax?
Yes. If you were required to file and miss the deadline, the initial £100 penalty applies even if you owe nothing or have already paid.
Can I still file on paper?
The paper deadline for 2025-26 was 31 October 2026, so most people should now file online.
Is 31 January 2027 really a Sunday?
Yes. The deadline stays 31 January, so do not leave the return or payment until the last weekend.
What if I realise I made a mistake after filing?
You can usually amend a return online, normally within 12 months of the filing deadline, which is 31 January 2028 for this return. The Low Incomes Tax Reform Group confirms the 2025-26 amendment date.
Sources: GOV.UK Self Assessment deadlines and penalties pages, Low Incomes Tax Reform Group. We are not licensed tax or financial advisers.
