Missing a tax filing date is something that you want to avoid. However sometimes there’s factors and obstacles out of your control that disrupt and prevent you from filing on time. 

Late invoices/proof-of-purchase, delayed payments or any one of the mountain of essential documents that always seem to mysteriously vanish at the last minute.

Not to mention everyday distractions like the kids’ sports-day or taking the dog to the vet.

Unfortunately filing a tax return or making a tax payment late results in being slapped with an immediate £100 penalty from HMRC. Which rises the longer your return remains unfiled/your payment remains unpaid.

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Can I appeal late filing penalties?

Yes, you can! If you have a reasonable and legitimate reason for missing the deadline, you can try to appeal the fine. HMRC generally gives you 30 days from the date on your penalty notice to do this.

For the common £100 late filing penalty, the easiest way to appeal is now through your HMRC online account. For other penalties, or if you can’t use the online service, you’ll need to use the SA370 form. 

We’ll explain how in a moment, but first, let’s break down the late filing and late payment penalties to show you why it’s worth appealing.

Penalties for delayed tax filings with HMRC

Penalty schedule for overdue tax payments with HMRC

How to appeal a Self Assessment penalty

As we mentioned, you have 30 days from the date of your penalty notice to appeal. There are a few ways to do it depending on your situation, including the SA370 form.

Method 1: appeal online

This is the quickest and easiest method for appealing the Self Assessment standard £100 late filing penalty. Here’s how you do it:

1. Log into your HMRC online account. 
2. Head to the section for appealing a penalty.
3. Provide the details of your “reasonable excuse”, explaining why your return was late.
4. Submit your appeal electronically. It’s as easy as that.

Method 2: Appeal by post with form SA370

If you need to appeal a penalty that's more than £100, or you can't use the online service for any reason, you'll need to download and fill out the SA370 appeal form.

Completing the form is straightforward, but requires attention to detail: 

• Personal details: Start by filling in your personal information, including your full name, address, and tax reference number.

• Reason for late filing/payment: Clearly state the reason for your delay. This should be a valid, genuine reason. Be specific and provide any relevant dates and details.

• Supporting evidence: Attach any evidence that supports your claim. This could be medical records, a letter from an employer, or proof of unforeseen circumstances.

• Declaration: Ensure you read the declaration section thoroughly before signing and dating the form.

Remember, the key is to be honest and provide as much detail as possible to substantiate your claim. We've included a screenshot below of what the form looks like.

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What happens next? HMRC’s response

Once HMRC receives your SA370 form, they will review your appeal. This process can take several weeks. HMRC will consider:

• The validity of your reason: Is the reason for your delay something genuinely out of your control?

• Timeliness of your appeal: Did you file the appeal within a reasonable time after the deadline?

HMRC will notify you of their decision by mail. If your appeal is accepted, the penalties will be waived. 

However, if your appeal is denied, you will be expected to pay the fines. In some cases, you might be able to request a further review if you believe the decision is unfair.

A new points-based system is coming

It’s worth knowing that HMRC is changing the penalty system for those who will be using Making Tax Digital for Income Tax. From April 6th 2026, all individuals with either a self-employed or personal rental income over £50,000 will need to follow the MTD for IT rules. 

HMRC plans to replace the current late filing and late payment penalties with a points-based system. Each missed quarterly submission or late payment will add points to your account, and reaching certain thresholds could trigger fines. 

However, this system will be delayed during the first year to give everyone time to get used to submitting quarterly updates. During this period, HMRC will focus on education and support rather than penalties, giving you a chance to adapt to the new routine before any points start to count.

A life-line for lateness

Filing taxes can sometimes be overwhelming, and missing a deadline can happen to the best of us. The SA370 form is a lifeline in such situations, allowing you to explain your circumstances and potentially avoid hefty fines. 

Remember, it's crucial to stay proactive, provide detailed information, and respond promptly to any HMRC correspondence following your appeal. With the right approach, you can navigate through this with minimal stress.

One affordable and simple solution to eliminate any chance of a missed filing is to use Crunch’s Self Assessment service. Our expert accountants will handle and submit your tax return for your, keeping it totally error free and saving you all the boring paperwork.