The self assessment deadline for filing your 2025/26 tax return online is 31 January 2027. It isn’t the only date that matters, though. If you need to file for the first time, HMRC needs to hear from you by 5 October 2026. Here is every date for the 2025/26 tax year (6 April 2025 to 5 April 2026), what happens if you miss one, and what to gather now.
Self assessment deadline dates for 2025/26
| Date | What’s due |
|---|---|
| 5 October 2026 | Register for Self Assessment if you have income or gains to report for the first time |
| 31 October 2026 | Paper tax returns due, including if you want HMRC to work out your tax for you |
| 30 December 2026 | Online returns filed by now can have tax under £3,000 collected through your PAYE tax code |
| 31 January 2027 | Online tax returns due; pay your 2025/26 balance and your first payment on account for 2026/27 |
| 1 February 2027 | Interest starts on any 2025/26 tax still unpaid |
| 31 July 2027 | Second payment on account for 2026/27 |
If HMRC sends you a notice to file after 31 October 2026, you have three months from the date of that notice instead. You can check the dates on GOV.UK.
Filing for the first time?
If you became self-employed, started letting a property or had other untaxed income in 2025/26, you must tell HMRC by 5 October 2026. You can register for Self Assessment on GOV.UK. Registration gives you a Unique Taxpayer Reference (UTR). If you’re stuck, our UTR registration service can do it for you.
How payments on account work
Payments on account are advance payments towards next year’s tax bill. Each one is normally half of the previous year’s bill, due on 31 January and 31 July.
You don’t need to make them if:
• your last Self Assessment bill was less than £1,000, or
• more than 80% of your tax was already collected at source, for example through PAYE.
First-time filers are often caught out. In January you pay your full 2025/26 bill plus the first payment on account for 2026/27. On a £3,000 bill, that is £4,500 due on 31 January 2027, then £1,500 on 31 July 2027. If you expect to earn less next year, you can ask HMRC to reduce your payments on account.
What happens if you miss the self assessment deadline
HMRC charges penalties for late returns, even if you owe no tax:
• £100 as soon as the return is late
• after 3 months, £10 a day, up to £900
• after 6 months, 5% of the tax due or £300, whichever is greater
• after 12 months, another 5% or £300, whichever is greater
Late payment adds 5% of the unpaid tax at 30 days, 6 months and 12 months. Interest also runs from 1 February 2027 at the Bank of England base rate plus 4%, currently 7.75% a year. See the full rules on GOV.UK.
Still haven’t filed for 2024/25? 31 January 2027 is your last chance to file it before the 12-month penalty applies. A new points-based penalty system is coming, but it only applies from April 2027, so your 2025/26 return falls under the rules above.
Sold property or shares? Capital gains dates
• UK residential property: report and pay any Capital Gains Tax within 60 days of completion, using a Capital Gains Tax on UK property account.
• Other gains, such as shares: report them on your 2025/26 tax return, or through HMRC’s real-time Capital Gains Tax service by 31 December 2026 and pay by 31 January 2027. If you already file a tax return, include them there too.
• Small gains: the tax-free allowance is £3,000 for 2025/26. If you file a tax return, you must still report your sales if they came to more than £50,000 in total, even when your gains are within the allowance.
Making Tax Digital: why this return matters
Sole traders and landlords with qualifying income over £50,000 in 2024/25 have used Making Tax Digital for Income Tax since 6 April 2026. If your 2025/26 income from self-employment and property, before expenses, is over £30,000, you’ll need to join from April 2027. HMRC uses this return to decide, so it’s worth getting it right.
Your 2025/26 Self Assessment checklist
• Access: your UTR, Government Gateway login (or the HMRC app) and National Insurance number
• Employment and pensions: P60, P45 if you changed jobs, P11D for benefits, pension statements
• Self-employment: sales records, expense receipts and mileage for 6 April 2025 to 5 April 2026
• Property: rent received, agent statements, mortgage interest, repairs and insurance
• Company directors: dividend vouchers and your company details
• Savings and investments: bank interest, dividends, and dates, costs and proceeds of anything you sold
• Reliefs: personal pension contributions, Gift Aid donations, Child Benefit received, student loan plan type
Let us take the deadline off your plate
KPN Accounting in Staines-upon-Thames prepares and files Self Assessment returns for sole traders, landlords and directors. We’re authorised tax agents, and we work out what you owe early, so January holds no surprises. Find out more about our Self Assessment tax returns service.
This article is general guidance based on HMRC information as of September 2026. It isn’t personal tax advice.