Self Assessment Penalties in the UK: What Happens If You File or Pay Late
Missing the Self Assessment deadline triggers automatic penalties that can add up quickly. HMRC imposes penalties for two distinct failures: late filing (not submitting your return on time) and late payment (not paying the tax you owe on time). These are independent — you can be penalised for both simultaneously, even if the other is fine. Here is every penalty level and how to avoid or appeal them.
The Self Assessment deadlines
- 31 October: Deadline for paper returns (if you still file on paper).
- 31 January: Deadline for online returns AND the payment of the balancing payment plus any first Payment on Account.
- 31 July: Deadline for the second Payment on Account.
Almost all taxpayers now file online, so the key date is 31 January each year.
Late filing penalties
| How late | Penalty |
|---|---|
| Up to 3 months late | Automatic £100 fixed penalty (regardless of tax owed or whether you have overpaid) |
| 3–6 months late | £10 per day, up to 90 days maximum = £900 additional (on top of the £100) |
| 6–12 months late | 5% of the tax liability OR £300, whichever is greater |
| More than 12 months late | A further 5% of tax liability or £300 (whichever is greater) if deliberate withholding, the penalty can rise to 70% or 100% |
The daily £10 penalties (after 3 months) are automatically charged by HMRC without the need for a separate assessment. You will receive a penalty notice. The total maximum penalty for filing a return more than 12 months late (where tax has been deliberately withheld) can exceed the tax liability itself.
Late payment penalties
These are separate from filing penalties and accumulate as follows:
- 30 days after the deadline: 5% surcharge on the outstanding tax.
- 6 months after the deadline: A further 5% surcharge.
- 12 months after the deadline: A further 5% surcharge.
So if you owe £4,000 and pay it 13 months late, the surcharges alone are £600 (3 × 5% × £4,000). In addition, interest accrues from the day after the payment deadline at HMRC's rate (currently 7.25% per annum in early 2025).
£100 penalty even if you do not owe any tax
One of the most frustrating features of the system: the initial £100 fixed penalty for late filing applies even if your tax liability is zero, or if you are actually due a refund. The penalty is for failing to file the return on time — not for failing to pay tax. You must file the return to avoid this penalty, regardless of your tax position.
Reasonable excuse and appeals
You can appeal against penalties if you have a "reasonable excuse" for the failure. HMRC accepts reasonable excuses including:
- Serious illness or hospitalisation of you or a close relative.
- Bereavement close to the deadline.
- Postal delays or HMRC system failures.
- A significant disruption beyond your control (e.g. fire, flood, theft of records).
HMRC does not accept: "I forgot," "I didn't know the deadline," "my accountant didn't tell me," or "I was too busy." Appeals must be made within 30 days of the penalty notice. If HMRC rejects your appeal, you can take the matter to the First-tier Tax Tribunal.
Payments on Account
If your tax bill is above £1,000 and less than 80% of your total tax was collected at source (via PAYE), HMRC requires you to make Payments on Account — advance payments of next year's estimated tax. There are two instalments: 31 January and 31 July, each equal to 50% of your previous year's tax bill. If you fail to pay these on time, interest accrues but there is no surcharge (only on the balancing payment).
Frequently asked questions
I missed the January deadline but filed the return in February. What will I owe?
You will owe the £100 fixed penalty for late filing, plus interest on any outstanding tax from 1 February. If you pay the tax within 30 days of the 31 January deadline, you avoid the 5% surcharge. File and pay as quickly as possible to minimise the damage — and consider whether you have a reasonable excuse to appeal the £100 penalty.