Millions face £100 HMRC fine ahead of self assessment deadline

The key tax deadline is January 31, but thousands of people celebrated the New Year by filing their Self Assessment tax return.

With less than a month to the January 31 deadline, 54,053 customers chose to ring in the New Year by filing their tax return for the 2024 to 2025 tax year on New Year’s Eve and New Year’s Day. The figures, show:

• 342 customers beat the bells by filing their tax return in the last hour of 2025
• 19,789 missed their traditional New Year’s Day walk or day in front of the TV to file their tax return instead
• 3,927 people filed between 11:00 and 11:59 on December 31 – the most popular time to file over the two days

More than 6.36 million taxpayers have submitted their tax return so far, which leaves almost 5.65 million who still need to complete their Self Assessment. Those who miss the deadline could face an initial late filing penalty of £100.

Myrtle Lloyd, HMRC’s Chief Customer Officer, says: “New Year is a great time to start afresh. What better way than to ensure your tax affairs are in order for another year than completing your tax return. If you have yet to start, the clock is ticking, go to GOV.UK and start today.”

A wide range of online help and support is available on GOV.UK to help people fill in and file their tax return.

Customers can start their tax return, save it and re-visit it as many times as they need to before they submit it. And, once they’ve sent it, the bill doesn’t have to be paid straight away, but does need to be paid before the January 31 deadline.

The easiest way to pay is through the HMRC app. Customers can also set up notifications in the app to ensure they know when payments are due so they don’t miss a deadline.

Information about different payment options can be found on GOV.UK .

Customers who are unable to meet the tax return deadline need to tell HMRC before January 31. Otherwise, the penalties for late tax returns are:

• an initial £100 fixed penalty, which applies even if there is no tax to pay, or if the tax due is paid on time
• after 3 months, additional daily penalties of £10 per day, up to a maximum of £900
• after 6 months, a further penalty of 5% of the tax due or £300, whichever is greater
• after 12 months, another 5% or £300 charge, whichever is greater

There are also additional penalties for late payments of 5% of the tax unpaid at 30 days, 6 months and 12 months. If tax remains unpaid after the deadline, interest will also be charged on the amount owed, in addition to the penalties above.

Do you need to do a #SelfAssessment tax return?

You might need to if you:

✅ Have earnt more than £1,000 through a side-hustle.
✅ Are self-employed.
✅ Rent out a property.
✅ Use cryptoassets.

Check if you need to register 🔗⬇️
pic.twitter.com/PBtJt5blpk

— HM Revenue & Customs (@HMRCgovuk) January 5, 2026

Sarah Coles, head of personal finance at Hargreaves Lansdown, adds: “The UK is a nation of last-minute procrastinators, hoping to sneak an eleventh-hour tax return under the wire.

“Almost half of people who need to do a self-assessment tax return by the end of the month hadn’t got round to it by the start of 2026.

“And while there’s nothing wrong with being motivated by a deadline, it raises the risk of something going awry.

“If you need to complete one, and haven’t got round to it yet, there are 10 last-minute checks to do – to make sure you’ve dodged the key tax return traps.

1. Check you have access to the system first: Make sure you have your Unique Taxpayer Reference number and can access the Government Gateway right now. If you haven’t registered for self-assessment, do it now, because your UTR will take up to 10 days to reach you by post. If you’ve not registered for the Gateway yet, it will take up to 10 days for your activation code to get to you. If you’ve forgotten or lost any of these things, you can recover them.
2. Beware of capital gains tax mistakes. If you sold assets like shares after October 30, 2024, the system won’t automatically calculate the correct amount of capital gains tax you have to pay. Annoyingly, you need to use the adjustment calculator on the Gov.UK website to make changes to the calculation.
3. Consider the impact of frozen tax thresholds. If a pay rise pushed you over the income tax threshold into paying higher or additional rate tax, the extra tax on your income may have been taken through the PAYE system, but it may also mean you have to complete a tax return. You may need to reclaim tax on pension contributions or charitable donations, or you may need to pay tax on your savings now your personal savings allowance has dropped.
4. Consider child benefit. The high-income child benefit charge kicks in at £60,000. If your income (or your partner’s) has pushed over the threshold since, and you receive child benefit, you will need to repay at least some of it through self-assessment. If you tick the box, it will calculate what you owe. If you only use this to pay the high interest child benefit charge, you can opt out and pay it through your tax code using the new PAYE digital service.
5. Don’t forget crypto. HMRC has been reminding people that gains from crypto need to be declared for capital gains tax purposes, if it took your total capital gains over your annual allowance, you will need to pay tax. If you made a loss, you’ll also need to complete a tax return if you want to offset it against gains in future years.
6. Remember gains from trading on sites like e-Bay and Vinted. This will only include things you have made or bought and sold for a profit – rather than items from a general clear-out. You also have an allowance of £1,000 if you’re selling for profit, but after that, you need to declare this by completing a tax return. These sites only started having to automatically disclose these gains to HMRC in 2024, but you are responsible for paying this tax.
7. Don’t rush the pensions bit. This is a common area for mistakes to happen. Higher rate taxpayers need to make sure they claim higher rate tax relief if it isn’t done automatically. For example, on a personal pension or SIPP you need to enter the gross value of contributions. This isn’t just a total of all the money you paid in: it includes the tax relief on top. For example, if you have contributed £800, the gross amount after tax relief is added is £1,000.
8. Check you have actually paid. You’d be surprised how many people are so focused on the admin that they forget this bit. If you owe tax, you need to pay this no later than January 31 or you’ll pay interest and a fine.
9. If you can’t afford your bill, see if you can use a time-to-pay arrangement, spreading your tax bill over the coming months. You should be able to do this online if you owe £30,000 or less, you’re within 60 days of the payment deadline, and you don’t already have a payment plan with HMRC. It will only be possible to set this up if HMRC thinks you can afford it, so it’s not a solution for everyone, and there is interest to pay on outstanding cash, but it’s a better solution than simply missing the payment and paying fines on top of interest.
10. Check whether you have to use Making Tax Digital for income tax from April 6 this year. Sole traders and landlords with a turnover of more than £50,000 will need to use it, so you’ll need to sign up as soon as possible. Getting started will give you time to get to grips with the software you have to use, and understand the new service. If the change starts to make the process too time-consuming, it gives you a chance to find an accountant to help too.

“While, you’re there, consider what your tax return has revealed about your finances: If you spent ages digging out details of interest payments, dividends or profits on share sales, consider consolidating to simplify things,” she adds.

“Use your tax return like a checklist: If you ended up paying tax on savings or investments, look for ways to shelter them from tax, like ISA and pensions.

“Not only can it save tax, but it also means you never have to bother with them on a tax return again.”

Recommended reading:

Do I have to fill in a tax return if I’m only paying back Child Benefit?

People who complete a Self Assessment tax return to pay the High Interest Child Benefit Charge (HICBC) can opt out and choose to pay it through their tax code via the new PAYE digital service.

Eligible customers need to notify HMRC to stop Self Assessment before the filing deadline.

Where a tax return has already been sent, customers can choose to stop from the following tax year. HMRC will then amend their tax code and they will be registered to pay HICBC through PAYE.

How about the 2025 Winter Fuel Payment for pensioners earning over £35,000?

Customers do not need to include their 2025 Winter Fuel Payment, or Pension Age Winter Heating payment in Scotland, on their tax return for the 2024 to 2025 tax year as payments received in Autumn 2025 will be recovered in the 2025 to 2026 tax return, due by January 31, 2027.

Self Assessment customers are at increased risk of being targeted by criminals and should never share their HMRC login details with anyone, including a tax agent, if they have one.