HMRC does not chase you to file your Self Assessment return on time. It just charges you if you do not. Penalties are automatic and start the moment you miss a deadline, whether or not you owe any tax.
Missing a deadline is easy to avoid. Here is what you need to know.
Disclaimer: This article is for general information only. Penalty rules and rates can change. Always check the current position at gov.uk or with a qualified accountant.
When is the Self Assessment deadline in the UK?
There are three key Self Assessment dates. Register by 5 October if you are new to Self Assessment or did not file last year. Submit a paper return by 31 October. File online and pay your tax bill by 31 January. All three dates fall after the end of the tax year they relate to.
For the 2025/26 tax year, which ended on 5 April 2026:
| Deadline | Date | What it covers |
|---|---|---|
| Registration | 5 October 2026 | Tell HMRC you need to file if you are new to SA |
| Paper return | 31 October 2026 | File by post |
| Online return + payment | 31 January 2027 | File online and pay the full tax bill |
Most people file online. The 31 January deadline covers both the return itself and any tax due. Payments on Account, which are advance payments towards your next year’s tax bill, are due on 31 January and 31 July.
What is the penalty for a late Self Assessment?
The late filing penalty has three stages. HMRC charges a £100 fixed penalty as soon as you miss the 31 January deadline. From 3 months late, HMRC adds £10 per day for up to 90 days. After 6 months, HMRC adds another penalty of 5% of the tax due, or £300 if that is higher. It applies again after 12 months.
In numbers, if your return is consistently late:
- 1 day late: £100 fixed penalty, automatically charged even if your tax bill is zero
- 3 months late (30 April): Daily £10 charges begin. These continue for up to 90 days and can add up to £900.
- 6 months late (31 July): 5% of your outstanding tax due, or £300 if that is higher.
- 12 months late (31 January): Another 5% of your outstanding tax due, or £300 if that is higher.
So a return filed two months late costs you £100. A return filed nine months late costs £100 + up to £900 in daily charges + 5% of tax owed. The penalties add up fast.
What is the penalty for late Self Assessment payment?
Late payment penalties are separate from late filing penalties. Interest starts the day after the payment deadline. After 30 days, HMRC adds a 5% surcharge on unpaid tax. HMRC adds another 5% at 6 months and again at 12 months. You can owe filing penalties, payment penalties, and interest at the same time.
Late payment penalties:
- Interest: Begins accruing from 1 February at HMRC’s current rate
- 30 days late (2 March): 5% surcharge on unpaid tax
- 6 months late (31 July): Additional 5% surcharge
- 12 months late (31 January): Another 5% surcharge
If you cannot pay your full bill by 31 January, contact HMRC before the deadline. HMRC’s Time to Pay service lets you agree a payment plan. Once it is agreed, penalties and interest on the amount covered by the plan are reduced or removed.
Can you appeal a Self Assessment penalty?
Yes. You can appeal a late filing or late payment penalty if you have a reasonable excuse. Reasonable excuses can include serious illness, bereavement, technical problems with the HMRC online system, or a natural disaster that stopped you from filing. Being busy, forgetting, or not knowing the deadline do not count.
You must appeal within 30 days of receiving the penalty notice. You can appeal online through your HMRC account or by writing to HMRC.
If HMRC rejects your appeal, you can ask for a review by an HMRC officer who was not involved in the original decision. If that also fails, you can take the matter to the Tax Tribunal.
What about Payments on Account?
If your Self Assessment tax bill is more than £1,000, HMRC usually asks for Payments on Account. These are advance payments towards your next year’s tax bill.
You pay half on 31 January, the same date as the return deadline, and half on 31 July. If your actual tax bill for the next year is lower, HMRC refunds the difference.
Payments on Account catch many first-time Self Assessment filers by surprise. In the first year you file, you may owe tax for the year just ended plus the first Payment on Account for the current year, both due on 31 January.
What if you miss the registration deadline?
Failing to register by 5 October is a separate offence called “failure to notify.” HMRC can charge a penalty based on the tax you owe. The longer you wait to register, the higher the potential penalty.
If you have missed the deadline, register now rather than later. Voluntary compliance before HMRC contacts you usually reduces the penalty.
How do you avoid Self Assessment penalties?
Keep it simple: file early, file online, and pay on time.
File early, as soon as HMRC opens the system in April. That gives you your tax bill months before it is due, so you can save for it instead of scrambling in January.
If you cannot pay the full amount by January, set up a Time to Pay arrangement before the deadline.
Using a self assessment filing service with an accountant means someone keeps an eye on the deadlines for you. Your accountant will chase the information they need, not the other way around.
DASA manages Self Assessment from start to finish
We handle the return, work out what you owe, remind you about payment deadlines, and deal with HMRC if anything comes up.
Get a quote and we will send you our current pricing through DASA’s self assessment service.