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Self Assessment Late Filing and Penalty Calculator
Missed the deadline? Enter your dates and the tax you owe to see the likely HMRC penalties and interest, so you know the cost of waiting.
Tax year 2025/26 · Last reviewed 20 October 2026 · Prepared by the accountants at Self Assessment Tax Return Accountants (a trading style of Accotax). About us
HMRC charges £100 if your return is even one day late, then £10 a day after 3 months (up to £900), then the greater of 5% of the tax due or £300 at 6 and 12 months. Late payment adds 5% at 30 days, 6 months and 12 months, plus interest (8% in this calculator).
How Self Assessment penalties work
A late return triggers an immediate fixed penalty. After three months, daily penalties start for up to 90 days. At six and twelve months, further penalties apply based on a percentage of the tax due or a fixed amount, whichever is higher. Late payment is charged separately, with penalties at 30 days, six months and twelve months, plus interest on the unpaid tax.
Why act now
Penalties grow with every day and month. Filing and paying as soon as possible limits the cost. If you had a good reason for the delay, you can appeal.
Rates used
| Personal allowance | £12,570 (reduced above £100,000) |
| Basic rate | 20% on the next £37,700 of taxable income |
| Higher rate | 40% up to £125,140 of taxable income |
| Additional rate | 45% above that |
| Class 4 National Insurance | 6% on profits between £12,570 and £50,270, then 2% |
| Trading allowance | £1,000 |
| Property allowance | £1,000 |
Rates for 2025/26, England, Wales and Northern Ireland. Check current HMRC guidance.
Worked examples
Late-filing penalties for a return with £5,000 of tax due (late-payment penalties and interest are extra):
| When you file | Late-filing penalties |
|---|---|
| 1 day late | £100 |
| 3 months late (filed) | £1,000 |
| 6 months late | £1,300 |
| 12 months late | £1,600 |
Common mistakes
- Assuming no penalty applies when no tax is due. The filing penalty still applies.
- Waiting for HMRC to send a reminder. They often do not.
- Not appealing when you had a reasonable excuse.
Related services and guides
Official sources
- Self Assessment penalties (GOV.UK)
- Self Assessment deadlines (GOV.UK)
- Appeal a penalty (GOV.UK)
Frequently asked questions
What is the penalty for filing a tax return one day late?
A late return normally triggers an immediate fixed penalty, even if it is only one day late and you owe no tax.
Can I appeal a penalty?
Yes. If you had a reasonable excuse, such as serious illness or a bereavement, you can appeal to HMRC.
Do I pay interest as well?
Yes. Interest runs on unpaid tax from the due date until you pay, at a rate HMRC sets.
Is this calculator exact?
It estimates penalties using the published rules. HMRC will confirm the exact amount, and special cases can differ.
What if I file late but owe nothing?
Late-filing penalties can still apply even when no tax is due, so file as soon as you can.
