You have a £100 penalty notice from HMRC. You want to appeal it. Before anything else, there are two things you must know: the return must be filed before HMRC will even look at your appeal, and you have 30 days from the date of the penalty notice to submit it.
Miss either of those and your appeal options narrow significantly. This guide walks you through the process in the correct order.
Step zero: file the return first
HMRC will not process a penalty appeal for an outstanding return. If your return is still unfiled, the appeal goes nowhere. File — even on estimated figures — before you do anything else.
Step 1: Check Your 30-Day Appeal Window
The penalty notice will have a date on it. You have 30 days from that date to submit a formal appeal. After 30 days, you can still appeal but you will need to provide an additional explanation for the delay — and HMRC will decide whether to accept the late appeal before even considering the grounds.
If you are already outside the 30-day window, do not assume it is too late. HMRC has discretion to accept late appeals where there was a good reason for the delay in appealing, and where there are also good grounds for the original appeal. Explain both.
Step 2: File the Return (If You Haven't Already)
This is non-negotiable. An appeal submitted before the return is filed will be held in abeyance or rejected outright. File the return — with estimates if necessary — before submitting any appeal paperwork.
If you are struggling to get records together, HMRC allows you to file with estimated figures and a note that an amendment will follow. Filing estimated figures stops daily penalty charges, removes the determination risk, and clears the way for your appeal to be processed.
Step 3: Complete the SA370 Form
The SA370 is HMRC's official penalty appeal form for Self Assessment. You can submit it online through your HMRC account, or download and post it. The form itself is not complex, but the section that matters most — the grounds for your appeal — is where most DIY attempts fail.
The SA370 asks you to select a reason for appeal from a dropdown (illness, bereavement, technical failure, etc.) and then provide a written explanation. The written explanation is where your appeal succeeds or fails. HMRC's caseworkers are looking for specific things:
- The exact dates of the preventing circumstance — when it started and when it resolved.
- Why specifically it prevented you from filing — not just that it was difficult, but that it was genuinely impossible.
- Evidence supporting the claim — referenced in the written explanation and attached.
- An explanation of why you filed when you did after the circumstances resolved — demonstrating you acted promptly.
Can you appeal online?
Yes — if you have a Government Gateway account, you can appeal directly through your HMRC Self Assessment account online. Select "appeal a penalty" from your account summary. The same 30-day deadline applies regardless of how you submit.
Step 4: Gather and Attach Evidence
The written explanation alone is not enough. HMRC expects documentation. What you need depends on your grounds:
Evidence required by excuse type
| Excuse | Evidence HMRC expects |
|---|---|
| Serious illness | GP or hospital letter with dates and confirmation of incapacity |
| Bereavement | Death certificate; GP letter if your own condition was affected |
| System failure | Screenshot of the HMRC error message with date visible |
| Fire or flood | Insurance claim reference, fire brigade report, or photographs |
| Theft / burglary | Police crime reference number; statement of what was taken |
Step 5: After You Submit
HMRC aims to respond to penalty appeals within 45 days. In practice it is often longer. During this time, the penalty is technically still on your account, but HMRC should not pursue enforcement while a formal appeal is in progress.
If HMRC rejects your appeal, they will write to you explaining why. At that point you have two further options: request an internal HMRC review (handled by a different caseworker), or appeal directly to the First-tier Tax Tribunal, which is an independent court that HMRC cannot influence. The Tribunal frequently overturns HMRC rejections where the original grounds were sound.
Paying the penalty does not kill the appeal
You can pay the £100 to avoid potential interest or enforcement action while your appeal is in progress, and still have the penalty repaid to you if the appeal succeeds. Paying is not an admission of liability.
Need your return filed urgently so you can appeal?
You cannot appeal until the return is in. Our specialists can have your return submitted within 48 hours — even with incomplete records — so your appeal window stays open.