Key takeaways
- A 2025/26 Self Assessment return filed after 31 January 2027 gets an initial £100 penalty, even if no tax is owed.
- After 3 months HMRC adds £10 a day up to £900, then 5% of the tax due or £300, whichever is greater, at 6 and 12 months.
- Late payment brings separate penalties of 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest.
- HMRC's late payment interest rate is base rate plus 4%, published as 7.75% from 9 January 2026.
- You usually have 30 days from the date a penalty is issued to appeal, and you need a reasonable excuse.
If your 2025/26 Self Assessment return is late, HMRC charges an initial £100 penalty the day after the 31 January 2027 deadline, even if you owe no tax. After 3 months it adds £10 a day up to £900, then 5% of the tax due or £300 (whichever is greater) at 6 months and again at 12 months, while paying late brings separate 5% penalties and interest.
This guide covers returns for the 2025/26 tax year (6 April 2025 to 5 April 2026), which are due online by 11:59pm on 31 January 2027. Every figure below was checked against GOV.UK on 17 September 2026.
Self Assessment penalties at a glance
| When | Late filing penalty | Late payment penalty |
|---|---|---|
| 1 day after the deadline | £100 | None yet, but interest starts |
| 30 days after the deadline | No new filing penalty | 5% of the tax still unpaid |
| 3 months after the deadline | £10 a day, up to a maximum of £900 | No new payment penalty |
| 6 months after the deadline | 5% of the tax due or £300, whichever is greater | 5% of the tax still unpaid |
| 12 months after the deadline | Another 5% of the tax due or £300, whichever is greater | 5% of the tax still unpaid |
The two sets of penalties are added together, so someone who files late and pays late gets both. Source: GOV.UK Self Assessment penalties.
Late filing penalties for 2025/26 returns
HMRC must receive your online return by 11:59pm on 31 January 2027. Paper returns for 2025/26 were due by 11:59pm on 31 October 2026, so a paper return that arrived after that date is already late. The penalties then build up in four steps:
- An initial £100 penalty. This applies even if you have no tax to pay or you pay your bill on time.
- £10 a day after 3 months. Daily penalties run for up to 90 days, a maximum of £900.
- A further penalty after 6 months of 5% of the tax due or £300, whichever is greater.
- Another penalty after 12 months of 5% of the tax due or £300, whichever is greater.
If a partnership return is late, every partner is charged a penalty.
If you registered for Self Assessment late
If you tell HMRC after 5 October 2026 that you need to file for 2025/26, HMRC sends a letter or email giving you 3 months from its date to send the return, so the filing penalties run from that later date. The tax itself is still due by 11:59pm on 31 January 2027. If you register after 5 October and do not pay all the tax by 31 January, you may also get a failure to notify penalty, based on the amount still unpaid.
Late payment penalties
Paying your 2025/26 tax late is penalised separately from filing late. HMRC charges 5% of the tax still unpaid at 30 days, at 6 months and at 12 months after the 31 January 2027 payment deadline. Because each penalty is worked out on the amount outstanding at that point, paying part of the bill early reduces the later penalties.
If you cannot pay in full, contact HMRC before the penalty dates. You may be able to set up a payment plan, also known as a Time to Pay arrangement (GOV.UK). Our guide to paying your Self Assessment tax explains the payment methods and how long each takes.
Late payment interest
HMRC also charges interest on any tax paid late, on top of the penalties. Late payment interest is set at the Bank of England base rate plus 4%, a margin that applies from 6 April 2025 (it was base rate plus 2.5% before then). HMRC's published rate for Income Tax is 7.75% from 9 January 2026, according to its interest rates page checked on 17 September 2026. The rate moves when the base rate changes, so check that page for the rate on the days your tax was unpaid.
Interest runs from the date the tax was due until the date it is paid. It also applies to payments on account paid late, and to extra tax that arises when a return is amended, where it normally runs from the original due dates (HMRC manual SALF305). A penalty that is not paid within 30 days of the date on the penalty notice also attracts interest.
Example: a return filed and paid 7 months late
Say your 2025/26 bill is £2,000 and you file and pay the whole amount 7 months after the 31 January 2027 deadline. Using the GOV.UK penalty rules:
| Penalty | Amount |
|---|---|
| Initial late filing penalty | £100 |
| Daily penalties after 3 months (90 days at £10) | £900 |
| 6 month filing penalty (5% of £2,000 is £100, so £300 applies) | £300 |
| Late payment penalty at 30 days (5% of £2,000) | £100 |
| Late payment penalty at 6 months (5% of £2,000) | £100 |
| Total penalties, before interest | £1,500 |
Interest would be added on the £2,000 for the 7 months it was unpaid. HMRC's penalty estimator gives an estimate for your own figures.
How to appeal a Self Assessment penalty
If you had a reasonable excuse, or you think the penalty is wrong, you can appeal. You usually have 30 days from the date the penalty was issued to contact HMRC or make an appeal. If you miss that deadline you will need to give a reason for the delay.
- Gather the date the penalty was issued, the date you filed your return and the date you paid, if you have.
- Write down your reasonable excuse, with dates, and why it stopped you filing or paying on time.
- Use HMRC's Self Assessment penalty appeal tool to appeal online, or download form SA370 or SA371 to appeal by post.
- If you have no appeal form, send a signed letter to HMRC explaining why the return or payment was late, with your name and Unique Taxpayer Reference (UTR).
HMRC suggests considering paying the penalty while you appeal. If you do not pay and the appeal is rejected, interest is charged on the penalty from the date it was due. If the appeal succeeds, HMRC repays what you paid with interest, as long as you have no other tax outstanding.
If HMRC does not change its decision, you will be offered a review by an officer who was not involved in the original decision, and you can also take your appeal to the tax tribunal (GOV.UK). Reviews usually take 45 days (GOV.UK reviews).
What HMRC accepts as a reasonable excuse
A reasonable excuse is something that stopped you meeting a tax obligation for a valid reason. GOV.UK gives these examples:
- your partner or another close relative died shortly before the deadline
- an unexpected stay in hospital that stopped you dealing with your tax affairs
- a serious or life-threatening illness
- your computer or software failed while you were preparing your online return
- problems with HMRC's online services
- a fire, flood or theft that stopped you completing your return
- postal delays you could not have predicted
- delays related to a disability or mental illness you have
- you were unaware of or misunderstood your legal obligation
- you relied on someone else to send your return, and they did not
Whatever the excuse, you must send the return or payment as soon as you are able to. HMRC will not accept that you did not have enough money to pay, that you found the online system too difficult, that you did not get a reminder, or that you made a mistake on your return (GOV.UK reasonable excuses).
If you have already missed the deadline
- File the return now. The daily £10 penalties only start after 3 months, and the 6 month penalty is avoidable, so every week counts.
- Pay what you can. Late payment penalties are 5% of whatever is still unpaid at 30 days, 6 months and 12 months, and interest runs daily.
- Ask for a payment plan if you cannot pay in full.
- Pay or appeal each penalty within 30 days of the date on the penalty notice (how to pay a penalty).
- Check you actually needed to file. If you did not need to send a return, you can ask HMRC to cancel the penalty (GOV.UK). Our guide on whether you need to complete a tax return covers the common cases.
If you realise after filing that the return was wrong, see how to amend a Self Assessment tax return. If your payments on account turn out higher than your final bill, see how to get a Self Assessment tax refund. The full calendar is in when is the next Self Assessment deadline.
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