Missed the 31 January 2027 Self Assessment deadline? See every late filing and payment penalty, a worked example, reasonable excuses and how to appeal.
The Self Assessment deadline for the 2025/26 tax year is 11:59pm on 31 January 2027, for both filing your online return and paying what you owe. Miss it and HMRC's penalties start immediately and keep growing. This guide sets out every late filing and late payment penalty from GOV.UK in one table, works through a realistic example, and explains what counts as a reasonable excuse and how to appeal.
If you are self-employed and not sure how big your bill will be, estimate it now with the free Self-Employed Tax Calculator.
Source: GOV.UK – Self Assessment deadlines and GOV.UK – Payments on account.
GOV.UK lists these penalties if you send your tax return late:
Late filing penalties are charged on top of anything you owe for paying late. If a partnership return is late, every partner is charged a penalty. Source: GOV.UK – Self Assessment penalties.
If you pay your tax late, GOV.UK says you'll get penalties of 5% of the tax unpaid at:
You are also charged interest on the amount you owe until it is paid. Source: GOV.UK – Self Assessment penalties.
Filing and payment penalties are separate, so you can get both.
Tom is a sole trader with a 2025/26 tax bill of £4,000. He files his return and pays in full at the end of August 2027, about seven months after the 31 January 2027 deadline.
Late filing:
Late payment:
Total penalties: about £1,700 plus interest on a £4,000 bill, more than 40% extra. Had Tom filed on time but paid late, he would have avoided £1,300 of it. The lesson: always file on time, even if you can't pay.
For a personal estimate, HMRC has an official penalty estimator. It does not account for payments already made, credits or earlier years' penalties.
If you should have registered for Self Assessment and register after 5 October, and then don't pay all your tax by 31 January, you may get a "failure to notify" penalty. It is based on the amount still unpaid, and you'll receive it within 12 months after HMRC gets your return. Source: GOV.UK – Self Assessment penalties.
You must pay a penalty within 30 days of the date on the penalty notice. Source: GOV.UK – Self Assessment penalties.
Late filing penalties are the biggest part of most penalty bills, and they are completely avoidable. If you can't pay in full:
If you know your tax will be lower than last year, for example because your profit has dropped, GOV.UK says you can ask HMRC to reduce your payments on account, online or by post. You'll need to give the amount you expect to make. Reducing them too far means a bigger balancing payment, and possibly interest, later. Source: GOV.UK – Payments on account.
You can challenge a penalty if you had a reasonable excuse: something that stopped you meeting a tax obligation for a valid reason. GOV.UK's examples include:
GOV.UK says these are not reasonable excuses:
You must send your return or payment as soon as you are able to once the problem ends. Source: GOV.UK – Reasonable excuses.
You usually have 30 days from the date the penalty was issued to appeal. If you miss that, you'll need to explain why. For Self Assessment, GOV.UK has a page on when and how to appeal a Self Assessment penalty. Give dates and evidence, such as hospital letters. If computer problems stopped you filing or paying, GOV.UK says to include the date you tried and details of any system error message. Source: GOV.UK – Disagree with a tax penalty.
£100 straight away, then £10 a day after 3 months (up to £900), then 5% of the tax due or £300 at 6 months and again at 12 months.
Yes. They are separate. Filing late and paying late can each lead to penalties, plus interest on unpaid tax.
5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest.
11:59pm on 31 January 2027 for online returns and payment. Paper returns were due by 31 October 2026.
No. GOV.UK says not receiving a reminder from HMRC is not a reasonable excuse.
Usually 30 days from the date the penalty was issued.
Penalties and deadlines were checked on GOV.UK in October 2026. This is general information, not tax advice. Contact HMRC or an accountant about your own situation.
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