What to do if you missed the self-assessment tax return deadline

An estimated 1.1 million self-assessors failed to file their 2022-23 tax return by the 31 January deadline, according to HMRC. They will now face a £100 fine, plus interest on any outstanding tax.

Of the 12.1 million customers expected to file this year, a whopping 778,068 waited until the last minute. The peak hour for filing on deadline day was between 4pm and 4.59pm, when 68,462 customers submitted their tax return. Yet there were 32,958 tardy taxpayers who literally left it until the eleventh hour and filed between 11pm and 11.59pm. 

Here, Which? explains what happens now if you missed the deadline and why you should get your tax return in as soon as possible.

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What's the penalty for filing late?

If you missed the deadline of midnight on 31 January, then you'll likely be slapped with a £100 fine. After that, you'll face the following penalties:

• Up to three months late: £10 each day, capped at 90 days (plus initial £100 fine)
• Six months late: a further 5% of the tax due, or £300, whichever is higher
• 12 months late: a further 5% of the tax due, or £300, whichever is higher

The only way HMRC might let you off the hook for late filing is if you have what is deemed a 'reasonable excuse'. 

While the tax office will weigh up appeals on a case-by-case basis, it will show leniency and waive any late fees if you have a compelling reason for missing the deadline. Excuses it considers legitimate include the recent death of a partner, an unexpected stay in hospital, or issues with HMRC's online services.

• Find out more: late tax returns and penalties for mistakes

Other fines you could face

Missing the filing deadline isn't the only reason why HMRC might charge a penalty.

Late payment

You’ll likely also face late payment charges if you haven't paid your tax bill – the deadline is also 31 January. 

You’ll be charged daily interest from the date the payment was due – currently 7.75% – and there may be further penalties if you're several months late paying your tax bill. Those are:

• Three months late: A charge equal to 5% of the tax due 
• Six months late: A further 5% charge
• 12 months late: Another 5% charge

Making a mistake

HMRC can also impose fines for mistakes, with penalties based on the amount of tax you owe and the kind of error HMRC deems you to have made. For example, whether it was simply a careless mistake or a deliberate attempt to hide something.

Penalties are calculated as follows:

• 0% charge: You've taken 'reasonable care' to fill out your tax return correctly
• 0-30% charge: You've been careless and made mistakes
• 20-70% charge: You've deliberately underestimated your tax
• 30-100% charge: You've deliberately underestimated your tax and tried to conceal it

In November 2023, we surveyed 508 people who were submitting a 2022-23 tax return and a third said 'worrying about making a mistake' was the aspect they disliked most about filing a tax return. And two in five falsely believed you can’t change a tax return form after it has been submitted.

The good news is that you can correct a tax return within 12 months of the self-assessment deadline. So try not to stress too much about making a silly mistake or two – the important thing now is to get your self-assessment form to HMRC as soon as possible.

• Find out more: important tax return deadlines in 2024

Ask for help if you're struggling

If you need a hand completing your tax return, then the HMRC website has plenty of information and step-by-step guides, including video tutorials and pre-recorded webinars. You can also use its digital assistant tool to ask for technical support if you're filing online.

Our survey found a third of self-assessors were concerned about being able to pay their tax bill this year. But if you're struggling to settle your bill, you may be able to set up a Time to Pay arrangement that lets you pay in instalments over an agreed period. You’ll pay interest on anything owed after the deadline, but at a lower rate than the late payment rate.

To set up a payment plan online, you'll need to owe less than £30,000, be within 60 days after the 31 January payment deadline, and not have any other payment plans or debts with HMRC. If these circumstances don’t apply to you, you can call the Payment Support Service on 0300 200 3835.

Which? also has a range of guides to take the pain out of the whole process, from tips on how to fill in a self-assessment tax return to advice on how to file online.

Try the Which? tax calculator

If you haven't filed your 2022-23 tax return yet, you can still use the Which? Tax calculator for the task.

You can calculate how much tax you owe from a range of income sources, and it will even suggest allowances and expenses you might have forgotten.

When you're ready, you can use the tool to file your tax return directly to HMRC.