What happens if I file my Self Assessment tax return late?

File your 2025-26 return online after 31 January 2027 and you get a £100 penalty straight away, then £10 a day after 3 months, and more at 6 and 12 months. Paying late adds 5% penalties and interest.

The 2025-26 tax year ran from 6 April 2025 to 5 April 2026. Its return is due online by 11:59pm on 31 January 2027, or on paper by 11:59pm on 31 October 2026, and the tax is due by 31 January 2027. If you registered after 5 October 2026, HMRC gives you a later filing deadline, 3 months from the date on its letter or email. The rules below follow GOV.UK as checked on 16 October 2026.

Late filing and late payment penalties

Filing late and paying late are two separate failures, and each has its own penalties. If you do both, you get both.

On top of the penalties, HMRC charges interest on tax paid late. GOV.UK gives the late payment interest rate as 7.75% from 9 January 2026, which is the Bank of England base rate plus 4%. The rate is linked to the base rate, so it changes when that does.

Worked example. A plumber owes £2,000 for 2025-26 and files online and pays on 15 September 2027, about seven and a half months late. Filing late costs £100, plus £900 in daily penalties, plus £300 at 6 months, because £300 is more than 5% of £2,000 (£100). That is £1,300. Paying late adds 5% at 30 days (£100) and 5% at 6 months (£100), so £200. The penalties come to £1,500, plus interest. This is an example only.

You must pay a penalty within 30 days of the date on the penalty notice. GOV.UK's penalty estimator can work out your own figures.

Reasonable excuse and appeals

If you have a reasonable excuse, you can appeal against a late filing or late payment penalty. GOV.UK gives examples of what may count:

• a partner or close relative died shortly before the deadline
• an unexpected stay in hospital, or a serious or life-threatening illness
• your computer or software failed while you were preparing your online return, or HMRC online services had problems
• a fire, flood or theft stopped you completing your return
• postal delays you could not have predicted

These will not count: a payment that failed because you did not have enough money, finding HMRC's online system too hard, not getting a reminder, or a mistake on your return. Even with a good excuse, you must file or pay as soon as you are able to.

You usually have 30 days from the date the penalty was issued to appeal. You can appeal online, or by post on form SA370 or SA371. If HMRC does not change its decision, you will be offered a review, and you can also take the appeal to the tax tribunal.

How this changes with Making Tax Digital

Making Tax Digital for Income Tax (MTD) brings new penalties that replace the ones above. They apply from the tax year you join MTD. Late filing earns penalty points, with £200 charged once you reach the threshold, and late payment penalties are charged at day 15 and day 30, then daily. Our guide to MTD penalties has the full rules and rates.

Who gets which rules depends on the tax year and on whether you are in MTD:

• Your 2025-26 return. The current penalties above apply to everyone, even if you joined MTD in April 2026.
• 2026-27, if you are in MTD. If you had to join on 6 April 2026, the new penalties apply to your 2026-27 return and payments. Volunteers agree to the new penalties when they sign up, HMRC writes to confirm when they start, and their threshold is 2 points instead of 4.
• 2026-27, if you are not in MTD. GOV.UK describes the new penalties as applying to people using MTD, and says anyone who becomes exempt during 2026-27 goes back to the current penalties.
• From April 2027. GOV.UK says the new penalties will apply to everyone who submits a personal Self Assessment return. Its penalty guidance, checked 16 October 2026, does not say which tax year's return that first covers for people outside MTD.

Late payment interest works the same way under both systems.

What this means for you

If you file your 2025-26 return online after 31 January 2027, you get the £100 penalty, whether or not you joined MTD. The penalties then grow, so a late return is always better sent sooner rather than later.

If you cannot pay in full, contact HMRC before the deadline. Under the current rules, HMRC's manual says that if HMRC agrees to let you pay later, no late payment penalty is charged on that tax from the date you asked, as long as you keep to the agreement. Interest still runs. Our guide to paying in instalments explains how.

Steps if your return is late or about to be

1. File the return as soon as you can, even if you cannot pay yet. The daily penalties start after 3 months.
2. Pay what you can by 31 January 2027 to cut the 5% penalties and the interest.
3. If you cannot pay in full, ask HMRC for a payment plan as early as you can, ideally before the deadline.
4. If something outside your control made you late, note the dates and keep the evidence.
5. Appeal, usually within 30 days of the date the penalty was issued, online or on form SA370 or SA371.
6. Run the free MTD check to see when the new points system starts for you.

There is more for tradespeople in the trades section and for landlords in the landlord section.