HMRC's deadline for paper Self Assessment tax returns falls on 31 October 2026 — three months earlier than the 31 January online cut-off most UK taxpayers plan around. For the 2025/26 tax year, which ended on 5 April 2026, the date applies to anyone filing a paper SA100 rather than using HMRC's online service or commercial software. And it catches people out every autumn precisely because it sits so far ahead of the deadline everyone actually talks about.
Getting hold of a paper form isn't automatic anymore, either. HMRC stopped mailing blank returns out to everyone some years ago, so taxpayers who want to file on paper generally have to request a form by phone or download and print one from GOV.UK before they can start filling it in.
Who still files on paper
Some taxpayers file on paper by choice. For others, there's little choice in the matter. Non-resident companies, trustees administering certain complex trusts, and people HMRC classifies as digitally excluded — because of age, disability, location, or a religious objection to using computers — are permitted or required to file on paper regardless of what the calendar says. Notably, HMRC's own guidance adds one more twist: anyone who receives a paper return after 31 July gets an automatically extended deadline of three months from the date of issue, rather than the fixed 31 October cut-off.
What happens if you miss it
Missing 31 October is not, on its own, the costly mistake many people assume. Self Assessment penalties attach to whichever deadline actually governs the return once it's filed, so a taxpayer who misses the paper cut-off can still switch to HMRC's online service and file by 31 January without a penalty — provided they register for online filing with enough time for HMRC to issue login credentials, which can take over a week by post. What does carry a fixed cost is missing both routes entirely:
- An automatic £100 penalty applies from one day after the return is late, even if no tax is actually owed.
- After three months, HMRC can add £10 a day, up to a maximum of 90 days.
- Six months on, a further charge of £300 or 5% of the tax due applies, whichever is higher.
- And the same again at twelve months, on top of interest that keeps accruing on any unpaid balance from 1 February.
HMRC's contact centres typically see call volumes climb through November and December, as taxpayers who missed the paper window scramble to arrange online access instead — a rush the department has been trying to shrink since Making Tax Digital for Income Tax began pulling sole traders and landlords earning above £50,000 into quarterly digital reporting from April 2026.