HMRC does not chase you to file on time. It just charges you if you miss the deadline. Penalties are automatic and start the moment you miss a deadline, regardless of whether you owe any tax.
Missing a deadline is easy to avoid if you know the dates. The main points are below. If you’re not sure whether you need to file, read our guide on self assessment requirements in the UK.
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 deadlines. Register by 5 October if you’re new to Self Assessment or didn’t file last year. Submit a paper return by 31 October. File online and pay your tax bill by 31 January. All three dates follow the end of the tax year they relate to.
For the 2025/26 tax year (which ended 5 April 2026):
| Deadline | Date | What it covers |
|---|---|---|
| Registration | 5 October 2026 | Tell HMRC you need to file, if 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 applies to both the return itself and any tax due. Payments on Account, 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?
Late filing penalties happen in three stages. A £100 fixed penalty applies straight after the 31 January deadline. From 3 months late, HMRC adds £10 a day for up to 90 days. After 6 months, a further penalty of 5% of the tax due (or £300, whichever is higher) applies and another after 12 months. HMRC sets out the full penalty structure on gov.uk.
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, adding up to £900 maximum.
- 6 months late (31 July): 5% of your outstanding tax due, or £300, whichever is greater.
- 12 months late (31 January): Another 5% of outstanding tax due, or £300, whichever is greater.
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 compound quickly.
What is the penalty for late Self Assessment payment?
Late payment penalties are separate from late filing penalties. Interest accrues from the day after the payment deadline. After 30 days, a 5% surcharge applies on unpaid tax. Further 5% surcharges apply at 6 months and 12 months. You can owe filing penalties, payment penalties, and interest simultaneously.
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 can’t pay your full bill by 31 January, contact HMRC before the deadline. HMRC’s Time to Pay service allows you to agree a payment plan. You can also pay your Self Assessment tax bill online through gov.uk. Once agreed, penalties and interest on amounts covered by the plan are reduced or waived.
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 include serious illness, bereavement, technical problems with the HMRC online system, or natural disasters affecting your ability to file. Being busy, forgetting, or not knowing the deadline are not accepted as reasonable excuses.
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 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 exceeds £1,000, HMRC usually requires 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 turns out to be 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’ve missed the deadline, register now rather than later. Voluntary compliance before HMRC contacts you reduces the penalty.
How do you avoid Self Assessment penalties?
Keep it simple: file early, file online, and pay on time. Once your return is in, read our guide on allowable expenses on self assessment.
Filing early, as soon as HMRC opens the system in April, means you know your tax bill months before it’s due. You can save for it rather than scrambling in January.
If you can’t 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 deadlines are tracked and met. Your accountant will chase you for the information they need, not the other way around.
DASA manages Self Assessment from start to finish
We handle the return, calculate your liability, remind you of payment deadlines, and deal with HMRC if anything comes up.
Get a quote and we’ll send you our current pricing, DASA’s self assessment service.