Last updated: 18 October 2026. I checked every one of these Self Assessment deadlines and penalties against HM Revenue and Customs (HMRC) pages on GOV.UK that day.
By Stiv · Design, technology and personal finance
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This is general information, not tax or financial advice. CoolCuration is not authorised by the Financial Conduct Authority. If your tax affairs are complicated, speak to a qualified accountant or tax adviser before you file.
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Paper returns are due on 31 October, online returns on 31 January
The Self Assessment deadlines for the 2025/26 tax year start with registration on 5 October 2026. After that, HMRC needs paper returns by 31 October 2026 and online returns by 31 January 2027. The tax bill is due on 31 January too, and some people pay a second instalment on 31 July 2027.
Saturday 31 October 2026, 11:59pm
HMRC must receive a paper tax return by then, so a form posted on the Saturday will arrive too late. If you miss it, you can still file online by 31 January 2027 without a late filing penalty. However, do not send a late paper return as well, because HMRC bases penalties on the first return it receives.
After that: Sunday 31 January 2027, for online returns and for paying the bill.