HMRC Penalty Calculator UK 2025 — Self-Assessment Late Filing & Payment Fines
Missing the 31 January self-assessment tax return deadline triggers immediate HMRC penalties that escalate rapidly the longer you delay. Use our free penalty estimator to calculate how much you may owe in late filing and late payment fines — and find out how to stop the penalties increasing.
HMRC also charges daily interest on unpaid tax. File your return immediately even if you cannot pay — this stops penalties increasing. Call HMRC on 0300 200 3310 or visit gov.uk/self-assessment-tax-returns.
HMRC Self-Assessment Penalty Structure
HMRC operates a tiered penalty system for late self-assessment returns and late payment of tax. Penalties increase rapidly the longer you delay — acting promptly is always in your interest.
Late Filing Penalties
| Delay | Penalty |
|---|---|
| 1 day late (from 1 February) | Automatic £100 fixed penalty |
| 3 months late (from 1 May) | £10 per day for up to 90 further days (up to £900 additional) |
| 6 months late | Additional penalty: 5% of tax owed OR £300, whichever is greater |
| 12 months late | Further penalty: 5% of tax owed OR £300, whichever is greater |
Late Payment Penalties
| Delay in Paying Tax | Penalty |
|---|---|
| 30 days late (after 2 March) | 5% of unpaid tax |
| 6 months late | Additional 5% of unpaid tax |
| 12 months late | Additional 5% of unpaid tax |
| Any unpaid amount | Daily interest at HMRC's current rate (currently 7.25% p.a.) |
Key Self-Assessment Deadlines 2024/25
- 31 October 2025 — Paper self-assessment return deadline for 2024/25
- 31 January 2026 — Online self-assessment return deadline for 2024/25
- 31 January 2026 — Balancing payment and first payment on account for 2025/26
- 31 July 2026 — Second payment on account for 2025/26
How to Appeal an HMRC Penalty — Reasonable Excuse
You can appeal an HMRC penalty if you have a genuine reason for missing the deadline — known as a "reasonable excuse." You must appeal within 30 days of the penalty notice using the HMRC online self-assessment service or form SA370.
What Counts as a Reasonable Excuse?
HMRC accepts the following as reasonable excuses:
- Serious or unexpected illness (of the taxpayer or a close relative)
- Bereavement of a close relative shortly before the deadline
- Unexpected hospital stay preventing you from completing your return
- Fire, flood, or theft affecting your records
- HMRC online service failures or technical issues on the deadline day
- Postal delays (for paper returns) outside your control
What Does NOT Count as a Reasonable Excuse?
- Not receiving a reminder from HMRC
- Not understanding the self-assessment system
- Relying on your accountant who missed the deadline (unless you had a genuine emergency)
- Having insufficient funds to pay the tax (though you can arrange Time to Pay)
Time to Pay Agreements
If you cannot pay your tax bill in full, contact HMRC immediately to arrange a Time to Pay agreement. HMRC will typically allow payment in monthly instalments over up to 12 months (sometimes longer for genuine financial hardship). Agreeing a Time to Pay does not remove penalties already incurred, but prevents further late payment charges while the arrangement is in place. Call HMRC's payment helpline on 0300 200 3835.