SA370: how to appeal the £100 late filing penalty (and when you'll win)
You can appeal a £100 late filing penalty using form SA370 (or online through your HMRC account) within 30 days of the penalty notice, and HMRC must cancel it if you have a 'reasonable excuse': something unexpected that stopped you filing on time, such as bereavement, serious illness, or HMRC's own system failures. You normally need to file the outstanding return before or alongside the appeal.
Written by the team behind Agent Arthur, our HMRC and tax specialist. This guide is general information about UK law, reviewed for accuracy.The £100 penalty, in plain terms
Miss the 31 January Self Assessment deadline and HMRC issues an automatic £100 penalty, even if you owed no tax, and even if you were only a day late. Around a million people receive it every year. It is not a judgement on you; it's a computer. And it is appealable.
Left unaddressed it gets worse: at 3 months late, £10 daily penalties start (up to £900); at 6 months, a further £300 or 5% of the tax due; at 12 months, another £300 or 5%.
How the appeal works
- Deadline: within 30 days of the date on the penalty notice (late appeals are possible with a good reason for the delay)
- Route: online via your Government Gateway account, or by post on form SA370
- File first: HMRC generally won't consider the appeal until the outstanding return is in, so file it, then appeal
- Say precisely what happened, when, and why it prevented filing, and that you filed as soon as you reasonably could afterwards
- If HMRC rejects it, you can request a statutory review or take it to the First-tier Tax Tribunal (free to lodge)
What a strong appeal letter contains
- The facts, dated: what happened, exactly when, and how it stopped you filing
- Why it fits 'reasonable excuse': unexpected, outside your control, and you acted as soon as you could once it passed
- Evidence: hospital letters, a death certificate, HMRC service-status screenshots, correspondence
- A polite, factual tone. Indignation doesn't cancel penalties; evidence does
Get your SA370 appeal drafted properlyArthur drafts a penalty appeal built around your actual circumstances and HMRC's own reasonable-excuse criteria, with the evidence checklist to attach.£5 launch price (normally from £19.99)Start my appeal letterCommon questions
What counts as a reasonable excuse for filing late?
HMRC's own examples include the death of a partner or close relative shortly before the deadline, an unexpected hospital stay or serious illness, computer or software failure while preparing the return, HMRC online service problems, fire, flood or theft, and postal delays. Disabilities and mental health conditions that affected you are also relevant.
What does HMRC refuse to accept?
Common rejections: relying on someone else who let you down (unless you took reasonable care), finding the online system too difficult, not receiving a reminder, or a bounced payment. 'I didn't know the deadline' rarely succeeds.
I owed no tax: do I still have to pay the £100?
The penalty applies even with zero tax due, which is exactly why so many people find it unfair. It's still appealable with a reasonable excuse, and worth appealing.
I missed the 30-day appeal window: is it over?
No. You can submit a late appeal explaining both the reasonable excuse for filing late AND the reason your appeal itself is late. HMRC accepts late appeals with good reason.
What happens after I appeal?
HMRC either cancels the penalty, or writes rejecting the appeal. If rejected, you can ask for an independent statutory review, and after that appeal to the First-tier Tribunal. Many penalty disputes settle at review.