Got an HMRC Penalty? Here's How to Appeal It Properly

A late-filing or late-payment penalty letter from HMRC isn't necessarily the final word. If you have a genuine reason for missing a deadline, you can challenge it — but only if you act quickly and make the right kind of case.

The 30-day window

You generally have 30 days from the date the penalty was issued to appeal, either online, using form SA370, or by letter, according to gov.uk's guidance on disagreeing with a tax decision. Miss that window and you'll need to explain the delay itself before HMRC will even consider your original appeal.

What actually counts as a "reasonable excuse"

HMRC's bar for a reasonable excuse is genuinely being prevented from meeting your obligation, not merely finding it inconvenient. According to guidance summarised by Landolio and Tax2u, examples that are typically accepted include serious illness or hospitalisation, bereavement of a close relative near the deadline, theft of your business records, unexpected postal delays, and documented HMRC technical failures — for instance if the online filing system was down when you tried to submit.

Excuses that are routinely rejected include forgetting the deadline, being too busy, not having enough money to pay, or relying on an agent who then failed without you following up. Being unaware you needed to file at all can sometimes carry weight, but is treated with more scepticism.

How to build your appeal

Your written explanation should cover four things clearly: what happened, exactly when it happened, how it stopped you meeting the deadline, and when you put things right once you were able to. Gather supporting evidence before you submit — hospital letters, a death certificate, a crime reference number, or a screenshot of an HMRC system error with a timestamp all strengthen a case, according to Taxfix's appeal guide.

What happens after you appeal

HMRC typically responds within a few weeks. If your appeal succeeds, the penalty is cancelled or reduced. If it's rejected, you're not out of options — you can ask for an internal review by a different HMRC officer, or escalate the matter to the independent Tax Tribunal, which is free to use without a solicitor for most cases.

Checklist: appealing an HMRC penalty

• Check the date on your penalty notice and count 30 days from it — mark the deadline immediately.
• Identify which category your reason falls into: illness, bereavement, theft, technical failure, or another genuinely unexpected event.
• Gather documented evidence before writing your appeal, not after.
• Submit via the online service, form SA370, or by letter, whichever suits your evidence best.
• Keep a copy of everything you send and note the date submitted.
• If rejected, request an internal review before considering the Tax Tribunal route.

Key Numbers

• 30 days — standard window to appeal an HMRC penalty from the date it was issued
• £100 — typical initial late-filing penalty for Self Assessment, before daily and further penalties accrue
• 0 — cost of escalating to the Tax Tribunal for most straightforward appeals without legal representation

Sources

• gov.uk: Disagree with a tax decision or penalty
• Landolio: How to appeal HMRC Self-Assessment penalties
• Tax2u: How to appeal a Self Assessment penalty
• Taxfix: Appealing an HMRC Self Assessment penalty

Educational content only — not financial advice.