Have a reasonable excuse for missing a Self Assessment deadline? Here’s how to appeal a penalty

Sometimes, life feels like an endless parade of tasks and deadlines that you have to remember. And it can be even worse as a business owner! Missing an important accounting date, like filing your Self Assessment tax return or paying your tax bill, could mean being hit with an unwelcome penalty from HMRC. 

It’s not all bad news - if you’ve received a Self Assessment penalty and have a reasonable excuse for missing the deadline, you can submit an appeal. These are the steps you can take if you disagree with a Self Assessment penalty.

Why might I be issued with a Self Assessment penalty?

The deadline for submitting your Self Assessment tax return in the UK is 31st January for online returns, or 31st October for paper tax returns - no exceptions. So, HMRC will almost certainly hand out a fixed Self Assessment penalty of £100 if you fail to meet your deadline. Heads up, the penalty will increase if you submit your return more than three months after the deadline. HMRC has a handy calculator you can use to estimate how much your penalty might be.

Anything else I should know?

Yes, that’s not the only reason HMRC may issue a penalty. If you miss the deadlines for paying your Self Assessment tax bill or for making payments on account you will also be charged. The amount of the penalty will depend on how late your payment is and how much tax you owe. HMRC’s calculator (above) can estimate the total cost of your penalty and any interest. 

Got it. So what is a reasonable excuse?

HMRC says a reasonable excuse is “something that stopped you meeting a tax obligation for a valid reason” - so, to pass muster, it must be an issue you couldn’t have reasonably avoided. Examples include medical issues, fire or flood damage, bereavement or serious computer failure. 

Fair warning, HMRC will expect you to submit your return and make any payments as soon as the reasonable excuse has been resolved. For example, you’re expected to file your tax return as soon as you’ve recovered from a medical issue.

What isn’t considered a reasonable excuse? 

Issues that HMRC will not accept as reasonable excuses include mistakes on your tax return, failing to pay because of a lack of funds or not receiving a reminder of the deadline.

So, I have a reasonable excuse and need to appeal a penalty. What next?

Before we get to the process - remember, HMRC will not accept your appeal until the Self Assessment tax return it relates to has been filed. If you haven’t submitted your return yet, do that immediately to minimise the penalty for late filing. HMRC also advises that it may help to pay the penalty even if you plan to appeal the decision. If you pay the penalty, you avoid any additional interest if your appeal is rejected. 

Okay, filing done. When should I appeal?

Appeals against Self Assessment penalties should usually be made (by you or someone authorised to act on your behalf) within 30 days of the penalty being issued. If you want to make an appeal after this deadline, you’ll need to clearly explain the reason for the delay when you appeal. 

Roger that. Now how do I process my appeal?

You have two options: 

Appeal your Self Assessment penalty online 

The easiest way to appeal against a late submission or late payment penalty is through your Government Gateway account. To submit your appeal, you’ll need:

• the date the penalty was issued
• the date you filed your Self Assessment tax return
• the details of your reasonable excuse 

Once you’ve successfully submitted your appeal online, make sure you wait until you see a confirmation message. It will include when you can expect to hear from HMRC with the result of your appeal.

Appeal your Self Assessment penalty by post 

Your other option is to appeal a late submission or late payment penalty by post. If you received your Self Assessment penalty in the post from HMRC, you can follow the instructions in the letter and use the enclosed appeal form. Alternatively, you can download and complete the SA370 appeal form and send it to HMRC with a letter outlining the details of your appeal. If you’re in a partnership, the nominated partner should appeal a late tax return for the partnership using form SA371.

If you don’t have an appeal form, you can send a signed letter to HMRC instead. The letter should include:

• the date the penalty was issued 

• the date you filed your Self Assessment tax return 

  • If technical problems prevented you from filing your return or paying your bill on time, you should include the date that you attempted to file or pay and details of the error message you received
• the details of your reasonable excuse 
• your Unique Taxpayer Reference (UTR) number

Appeal letters and forms should be sent to:

Self Assessment, HM Revenue and Customs, BX9 1AS

Okay, I’ve submitted my appeal. Now what?

Whether you made your appeal online or by post, HMRC will write to inform you if your appeal is successful. If HMRC agrees with your appeal, the penalty will be cancelled and, if you have already paid the penalty in full, the amount you paid will be refunded to you with interest from the date you made payment. 

If HMRC doesn’t agree with your appeal, you will receive a letter explaining the reason for their decision - as well as requesting payment for the penalty, if you haven’t already paid it. 

Hold up. What if my appeal is rejected, but I disagree with their decision?

If you disagree with HMRC’s decision, you will be offered a review with an officer from HMRC’s Solicitor’s Office and Legal Services directorate. If the outcome remains unchanged and you still disagree with the decision, you may then appeal to the tax tribunal. 

What if I don’t need to submit a tax return anymore?

If you received a Self Assessment penalty but you no longer need to submit a tax return, the penalty can be cancelled by HMRC. You can notify HMRC that you don’t need to file a tax return through the HMRC website or via their helpline.  

Can FreeAgent help me avoid a penalty palaver? 

Absolutely. FreeAgent’s unique Tax Timeline gives you live updates of your tax calculation and upcoming deadlines - so you can feel more confident about Self Assessment and avoid any nasty surprises. Try a 30-day free trial to see for yourself.

Originally published 14 February 2023
Last updated 31 January 2025