Self-Assessment: Late Filing Penalties and Appeals

Sometimes, even with the best intentions, you may miss the deadline for submitting your self-assessment and paying any tax owed. While the best plan is always to ensure you factor in enough time to meet these deadlines, it’s helpful to know what happens if you don’t and how to rectify any mistakes you may have made on your tax return.

When do I need to file my self-assessment tax return by? 

The first thing to do is have the deadline of 31 January marked in your diary. You must have filed your online self-assessment by midnight on this day and paid any tax due each year. You can still file a paper tax return, but in this case, you’ll have to do so by 31 October of the previous year. Read our guide on how to prepare your tax return if you're ready to file.

What happens if I miss the self-assessment deadline? 

Anyone who misses the 31 January filing deadline will receive a fixed £100 penalty. This will apply even if you’re not due to pay any tax. If you still haven’t submitted three months after the deadline, you’ll face a daily penalty of £10 for up to 90 days. If you leave it to six months overdue, you’ll be charged an additional £300 or 5% of the tax due, whichever is higher. Once it’s 12 months late, you’ll receive an extra £300 fine or 5% of the tax due. In the most serious cases, you may be fined 100% of the tax due.

If you’re part of a business partnership, all partners can be charged a penalty if a partnership tax return is filed late.

In addition to this, you’ll also have to pay interest on the tax due if you don’t pay by 31 January. HMRC currently charges interest at 3.25%.

One thing to be aware of here is that if you make payments on account, your interest payments may be higher than expected as you’ll be paying towards your tax for the following year.

Making an appeal for a late tax return penalty

If you receive a penalty for filing your tax return or making a payment late, the first thing to do is check that it’s correct. If it isn’t, then you can appeal to have it cancelled. You’ll need to complete an SA370 form within 30 days of the date shown on the penalty notice, or you can send a letter to HMRC explaining the situation. If you haven’t already, you should submit your return and/or pay your tax in the meantime.

Reasonable excuses for filing late 

If you did file late, there are several reasonable excuses accepted by HMRC that will mean you won’t have to pay a penalty. Examples given by HMRC are:

• your partner or another close relative died shortly before the tax return or payment deadline
• you had an unexpected stay in hospital that prevented you from dealing with your tax affairs
• you had a severe or life-threatening illness
• your computer or software failed just before or while you were preparing your online return
• service issues with HMRC’s online services
• a fire, flood or theft prevented you from completing your tax return
• postal delays that you could not have predicted
• delays related to a disability you have

Excuses that HMRC does not deem reasonable include someone else failing to submit the return on your behalf, payment failing because of insufficient funds and making a mistake on your tax return.

Penalties for making a mistake on your tax return 

Of course, mistakes can happen, and HMRC does take this into account. If you do make a mistake on your tax return, there is a series of penalties that can be charged in addition to the tax you owe.

If HMRC believe you took reasonable care to complete the return correctly, there’ll be no interest to pay. If you are seen as having been careless, the penalty will be between 0% and 30% of the extra tax owing. If HMRC conclude you have deliberately underestimated your tax, the penalty is between 20% and 70%, and if you are found to have deliberately underestimated your tax and attempted to conceal it, the penalty will be between 30% and 100%.

Find out more about penalties and appeals in our guide.

Correcting mistakes on your tax return 

If you realise you’ve made a mistake on your tax return, you can make changes to it within 12 months of the 31 January deadline, although you must have submitted it on time. So, for the 2020-2021 tax year, you’ll need to make changes by 31 January 2023. If you missed the deadline, you might still be able to make changes, but you’ll have to write to HMRC.

Otherwise, if you submitted your return online, you can sign in to your account, navigate to ‘tax account’ and choose ‘More details about your self-assessment returns and payments’. You’ll then see the option to amend your self-assessment. On this page, you’ll also be able to make payments and appeal late filing or late payment penalties should you need to.

If you filed a paper return, you’d need to download a new tax return and send HMRC the pages that need correcting. Write ‘amendment’ on each corrected page, and make sure that you include your name and your Unique Taxpayer Reference, which will be stated on any correspondence from HMRC. Send it to HMRC at the address found on your self-assessment paperwork.

If you only realise you need to make a correction after the deadline has passed, you can still write to HMRC stating the tax year involved, the reason and how much you think you have over-or under-paid.

What if HMRC has made a mistake?

If you think you’ve paid too much tax because of an HMRC mistake, you should be able to reclaim the full amount within four years of the end of the tax year you’re claiming for. To do this, you must contact HMRC in writing and specify that you are claiming overpayment relief, highlighting the year in question, the amount you think you’ve overpaid and why this may have happened. You should also state if you’ve previously made an appeal with the payment or assessment and include a signed declaration that the information you’ve given is “correct and complete to the best of your knowledge”. You must also have documentary proof of tax deducted, as you may need to provide this later. If your claim is successful, a refund will be sent to your bank account within four weeks.