Every year, millions of people across the UK file a Self Assessment tax return — sole traders, landlords, company directors and anyone with income that HMRC has not already taxed. The process is straightforward, but the deadlines are not forgiving: file even a day late and a £100 penalty applies automatically, even if you owe no tax at all.
This guide explains who must file a return, the Self Assessment tax return deadlines for the 2025/26 tax year, the penalties for filing or paying late, and the practical steps to get your return filed on time.
Who Must File a Self Assessment Tax Return?
You will usually need to file a tax return if any of the following apply to you:
- You are self-employed as a sole trader and your turnover was more than £1,000 (the trading allowance).
- You rent out property in the UK or abroad.
- You are a company director, or a partner in a business partnership.
- You have untaxed income, such as dividends, savings interest above your allowances, or income from abroad.
- You need to claim certain tax reliefs, or you owe tax through the High Income Child Benefit Charge.
- You have made a capital gain, for example by selling a second property or shares.
If HMRC has sent you a tax return, or a notice to file one, you must send it back — even if you think you have no tax to pay. The way many sole traders and landlords report their income is also changing: Making Tax Digital for Income Tax will require quarterly updates for those with qualifying income over £50,000 from April 2026, and over £30,000 from April 2027.
Self Assessment Tax Return Deadlines: Key Dates for 2025/26
The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. Here are the Self Assessment tax return deadlines to put in your diary:
- 5 October 2026 — the deadline to register for Self Assessment if you are filing for the first time.
- 31 October 2026 — the deadline for paper tax returns.
- 31 January 2027 — the deadline for online tax returns and for paying the tax you owe for 2025/26, as well as your first payment on account for 2026/27.
- 31 July 2027 — your second payment on account for 2026/27.
If you miss the Self Assessment tax return deadlines, interest starts to build on anything you owe, and the late filing penalties begin immediately.
Payments on Account: 31 January and 31 July
Many people in Self Assessment pay their tax in two instalments called payments on account, due on 31 January and 31 July. Each instalment is normally half of your previous year’s tax bill. The first payment on account for 2026/27 is due on 31 January 2027 — the same day you pay the tax for 2025/26.
Payments on account apply when your tax bill is more than £1,000 and less than 80% of it is collected at source. If your income falls, you can apply to reduce your payments on account — but be careful: if you reduce them too far, HMRC charges interest on the shortfall.
Penalties for Filing Late
The penalties for missing the Self Assessment tax return deadlines are automatic and they add up quickly:
- One day late: an immediate £100 penalty, even if you owe no tax.
- Three months late: £10 a day for up to 90 days, on top of the £100 — up to £900 more.
- Six months late: a further penalty of 5% of the tax due, or £300 if that is greater.
- Twelve months late: another 5% of the tax due, or £300 if that is greater — and more if HMRC believes you deliberately withheld information.
Paying late carries its own penalties too: 5% of the tax unpaid after 30 days, 6 months and 12 months, plus interest on the amount owed. If you have a genuine reason — a serious illness, a bereavement or a problem with HMRC’s own systems, for example — you can appeal on the grounds of a reasonable excuse.
How to File Your Return in Five Steps
- Register for Self Assessment. If this is your first return, tell HMRC by 5 October 2026. You will receive a Unique Taxpayer Reference (UTR) and can set up a Government Gateway account.
- Gather your records. Collect details of your income and any allowable expenses you plan to claim. Keep records of what you spend so you can claim only what you are entitled to — and keep them for at least five years after the 31 January filing deadline.
- Fill in the return. File online through your HMRC online account or Government Gateway. The online form guides you through each section: employment, self-employment, property, savings, dividends and other income.
- Check and submit. Review the figures before you submit. You can usually amend a return within 12 months of the 31 January deadline if you spot a mistake.
- Pay what you owe by 31 January 2027. Pay online by bank transfer, debit card or through your bank. Payments by cheque take longer, so allow extra time.
Frequently Asked Questions
Do I still need to file a return if I owe no tax?
Yes, if HMRC has asked you to file one. The £100 late filing penalty applies even when no tax is due.
Can I change a tax return after I have filed it?
Yes. You can usually amend your return within 12 months of the 31 January filing deadline — for the 2025/26 return, that is up to 31 January 2028.
What happens if I miss the 31 January deadline by one day?
The £100 penalty applies from the day after the deadline. File as soon as you can — the penalty will not increase for the first three months, but interest runs on any tax owed.
Is the payment deadline the same as the filing deadline?
Yes. Both the online filing deadline and the deadline for paying the tax are 31 January. Your first payment on account for the current tax year is also due on that day.
How We Can Help
Self Assessment involves more than filling in a form — it is about claiming what you are entitled to, keeping the right records and meeting the Self Assessment tax return deadlines. Financial Accounting Firm prepares tax returns, helps sole traders, landlords and directors stay on top of their obligations, and can take the whole process off your hands. Contact us to discuss your tax return. You can also read about our tax return services on our Services page.
This article is general information only and should not be taken as personal tax or financial advice. Tax rules can change, and your position will depend on your own circumstances.
