The Self Assessment tax return, 2025 to 2026
For the 2025 to 2026 tax year, register by 5 October 2026, send a paper return by 31 October 2026, or file online and pay by 31 January 2027. A second payment on account is due 31 July 2027. Filing late costs £100 straight away.
Last updated 16 Oct 2026 · Joel Lister, founder of Radar
Who this is for: anyone who sends a Self Assessment tax return, or thinks they may need to: sole traders, landlords, company directors and anyone HMRC has written to.
Who it is not for: deciding whether you must file, which GOV.UK’s own checker answers, or Making Tax Digital’s quarterly updates, which have their own dates.
| Deadline | What | Source |
|---|---|---|
| 5 October 2026 | Tell HMRC you need to complete a return for 2025 to 2026, if you have not sent one before | GOV.UK |
| 31 October 2026 | Paper returns must reach HMRC by 11:59pm | GOV.UK |
| 31 January 2027 | Online returns by 11:59pm, and the tax owed paid | GOV.UK |
| 31 July 2027 | Second payment on account, if you make payments towards your bill | GOV.UK |
How to send it
- Check you need to. You must send a return if HMRC asks you to; GOV.UK’s checker covers the rest (GOV.UK).
- Register by 5 October if it is your first return (GOV.UK).
- Fill it in after 5 April, the end of the tax year it is for, and file it online; the paper form is the SA100 (GOV.UK).
- Pay by 31 January, with any payment on account for the next year.
What being late costs
- Filing late: an initial £100 penalty; 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 (GOV.UK).
- Paying late: penalties of 5% of the tax unpaid at 30 days, 6 months and 12 months, and interest on the amount owed (GOV.UK).
Every date for the year, including payments on account, is on the Self Assessment dates page. Running a company as well? The company deadlines calculator has its Companies House and HMRC dates.
What Radar does with this
- Life setup asks: “Do you file a Self Assessment tax return?” The online deadline is 31 January. Radar reminds you two months ahead. Radar reminds you 60 days ahead.
- Life setup asks whether you file a Self Assessment return and puts 31 January on your Radar with a reminder two months ahead, every year, beside the work that has to fit around it.
Radar reads the calendars, task lists and CRM you connect, and the dates you give it. It writes back only when you press a button, and it never sends anything by itself.
Limitations and status
- Radar does not file your return or calculate your tax. It holds the dates and reminds you in good time.
- These are the 2025 to 2026 dates; GOV.UK’s page is the one to follow for later years.
Also free: Radar Lite, the habit tracker on its own, for you and anyone 13 or over in the family.
Questions
When is the Self Assessment deadline?
For 2025 to 2026: 31 October 2026 for paper returns, and 31 January 2027 for online returns and paying the tax. (GOV.UK)
When do I need to register for Self Assessment?
By 5 October after the end of the tax year, so 5 October 2026 for 2025 to 2026, if you need to complete a return. (GOV.UK)
What is the penalty for a late tax return?
An initial £100, then £10 a day after 3 months (up to £900), then 5% of the tax due or £300 after 6 and 12 months, whichever is greater. (GOV.UK)
When is the second payment on account due?
31 July, so 31 July 2027 for 2025 to 2026, if you make payments towards your bill. (GOV.UK)
Sources
- Self Assessment tax returns: deadlines, read 16 Oct 2026
- Self Assessment tax returns: penalties, read 16 Oct 2026
- Self Assessment tax returns, read 16 Oct 2026
- Check if you need to send a Self Assessment tax return, read 16 Oct 2026
Written by Joel Lister, founder of Radar · first published 16 Oct 2026. Radar is made by Neos Technologies Ltd.