Missed the Self Assessment Deadline? Here's What Happens
Quick Answer
Missing the Self Assessment deadline triggers an immediate £100 penalty, even if you owe no tax. Penalties increase the longer you delay — daily charges after 3 months, then percentage-based penalties after 6 and 12 months. Filing as soon as possible always limits the damage.
Late Filing Penalties
| How Late | Penalty |
|---|---|
| 1 day | £100 (fixed, even with no tax owed) |
| 3 months | £10 per day, up to £900 (90 days) |
| 6 months | 5% of tax due, or £300, whichever is greater |
| 12 months | A further 5% of tax due, or £300, whichever is greater |
Late Payment Penalties
These are separate from late filing penalties. If you pay your bill late, additional penalties of 5% of the unpaid tax can apply at 30 days, 6 months, and 12 months after the payment due date, on top of the filing penalties above.
Interest on Late Payment
HMRC charges interest on unpaid tax from the original due date until it's paid in full, regardless of any penalties. This applies even if you've arranged a Time to Pay plan — interest continues to accrue on the outstanding balance.
Reasonable Excuse
You can appeal a late filing or payment penalty if you have a reasonable excuse, such as serious illness, a family bereavement close to the deadline, or a failure of HMRC's own online services. Appeals are usually submitted within 30 days of the penalty notice, and you should still file and pay as soon as possible while the appeal is considered.
What to Do Now
- File your return immediately — even a late return limits further daily and percentage penalties
- Pay as much as you can toward your bill now to reduce interest
- If you can't pay in full, contact HMRC to discuss a Time to Pay arrangement
- Keep evidence if you plan to appeal on reasonable excuse grounds