Key takeaways
- The online Self Assessment deadline for the 2025/26 tax year is 11:59pm on 31 January 2027, and the tax is due the same day.
- Paper returns for 2025/26 were due by 31 October 2026, and new filers had to register by 5 October 2026.
- A late return costs £100 immediately, then £10 a day after 3 months, up to £900.
- Payments on account for 2026/27 fall on 31 January 2027 and 31 July 2027.
The next Self Assessment deadline is 11:59pm on 31 January 2027. That is the deadline to file your online tax return for the 2025/26 tax year (6 April 2025 to 5 April 2026) and to pay the tax you owe for it. Paper returns for 2025/26 were due by 31 October 2026.
Self Assessment deadlines for the 2025/26 tax year
| Deadline | What is due |
|---|---|
| 5 October 2026 | Tell HMRC you need to file a return, if you have not filed one before |
| 31 October 2026 | Paper tax return |
| 30 December 2026 | Online return, if you want the tax collected through your PAYE tax code |
| 31 January 2027 | Online tax return, plus payment of the tax owed for 2025/26 and any first payment on account for 2026/27 |
| 31 July 2027 | Second payment on account for 2026/27 |
All deadlines are 11:59pm on the day. Source: GOV.UK Self Assessment deadlines.
If you registered late
If you tell HMRC after 5 October 2026 that you need to file, HMRC gives you a different deadline to send your return: 3 months from the date on its letter or email. The tax itself is still due by 31 January 2027, so interest and late payment penalties can apply even though the return is not yet late.
What happens if you miss the deadline
HMRC's penalties for a late 2025/26 return are:
- 1 day late: an initial £100 penalty.
- 3 months late: £10 a day added, up to a maximum of £900.
- 6 months late: a further 5% of the tax due or £300, whichever is greater.
- 12 months late: another 5% of the tax due or £300, whichever is greater.
Paying late is penalised separately: 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest on the amount owed. If you had a reasonable excuse you can appeal a penalty. Source: GOV.UK penalties.
Payments on account
If your Self Assessment bill is £1,000 or more and less than 80% of your tax was taken at source, HMRC also asks for two payments on account towards the next year, each half of this year's bill, due on 31 January and 31 July. In your first year this makes January expensive. A sole trader with £45,000 of profit in 2025/26 and no other income owes £8,431.80 (Income Tax £6,486.00 and Class 4 National Insurance £1,945.80), so on 31 January 2027 they pay £12,647.70, including a first payment on account of £4,215.90, then £4,215.90 on 31 July 2027. See payments on account explained.
Who has to meet the deadline
You must file a 2025/26 return if, in that tax year, you were a sole trader earning more than £1,000, a partner in a business partnership, had Capital Gains Tax to pay (including on crypto), had to pay the High Income Child Benefit Charge outside PAYE, or had untaxed income such as rent, tips and commission, savings interest, dividends or foreign income (GOV.UK). Our guide on whether you need to complete a tax return covers the common cases.
The deadline after this one
The same pattern repeats each year. Returns for the 2026/27 tax year (6 April 2026 to 5 April 2027) will be due online by 31 January 2028. Sole traders and landlords with qualifying income over £50,000 have also had to use Making Tax Digital for Income Tax since 6 April 2026, sending quarterly updates through compatible software during 2026/27.
Get your return filed before 31 January
GoForma's ACCA and AAT qualified accountants prepare and file Self Assessment returns for a fixed £198 plus VAT, with HMRC enquiry support included, and have filed more than 7,000 tax returns. Crypto returns are £298 with a Koinly licence for up to 25,000 transactions. See our Self Assessment tax return service or book a free consultation.
