How do I appeal an HMRC late filing penalty?

You can appeal a Self Assessment late filing penalty within 30 days of the penalty notice, either online through your personal tax account or by post using form SA370, by showing a reasonable excuse that applied throughout the delay and that you filed as soon as it was resolved.

HMRC accepts genuine, unexpected events outside your control: a close bereavement near the deadline, a serious or life-threatening illness, an unforeseen hospital stay, a fire or flood that destroyed records, or HMRC's own online service failing on the day. Being unaware of the deadline, relying on someone else without checking, or simply being busy are not normally accepted.

The excuse must cover the whole period of the delay, and you must have filed the return without unreasonable further delay once the excuse ended, so an illness in November does not excuse a return still outstanding the following June.

Appeals must normally be made within 30 days of the date on the penalty notice, though HMRC has discretion to accept a late appeal with a good reason for the delay itself. Submit the appeal online, by SA370, or by letter, setting out the excuse, the dates involved and the date you actually filed.

If HMRC rejects the appeal, you can ask for an internal review or appeal to the tax tribunal within further set time limits. Penalties already paid are refunded if a later appeal succeeds, so it is worth appealing promptly rather than simply paying and moving on where a genuine excuse exists.

Rates, thresholds and deadlines quoted here reflect the 2026/27 UK position and current Companies House and HMRC guidance. Check GOV.UK, or ask us, before relying on them for your own company.