Households across the UK face being fined £100 by HM Revenue and Customs (HMRC) from January if they miss a looming deadline.

There’s now only a matter of weeks to go for Self Assessment tax returns for the 2024 to 2025 year to be filed and paid, with the deadline set for 11.59pm on January 31, 2026. According to HMRC, 37,435 people filed their tax returns between Christmas Eve and Boxing Day, but those who have yet to submit theirs now only have a month left. Those who file before December 30 may have the option of paying any tax owed through their PAYE tax code, and filing early also means more time to explore payment options if needed.

HMRC is now urging Self Assessment customers who are yet to file their tax return to start it today, as those who miss the January 31 deadline will be hit with a fixed £100 late filing penalty – even if there’s no tax to pay.

After three months those who still haven’t filed their tax return will face an additional penalty of £10 per day, up to a maximum of £900. 

This will increase yet again after six months with a further penalty of 5% of the tax that is due, or £300 – whichever is higher. After 12 months, another 5% – or £300 – will be added.

If the tax remains unpaid after the deadline, interest will also be charged on the amount that is owed, in addition to the extra penalties.

HMRC said: “You must submit your online tax return by 11:59pm on 31 January 2026 or you’ll get a late filing penalty. If you want to pay your Self Assessment bill through your tax code, you must submit it by 11:59pm on 30 December 2025. If you miss this deadline, you’ll have to pay another way. 

“You can submit your return any time on or after 6 April 2025 up to the deadline.”

Reasons for not paying your tax bill, or arranging a payment plan, by the January 31 deadline will be considered individually and only those who provide a reasonable excuse may avoid a penalty, while those without will face a fine.

HMRC says a reasonable excuse can include any of the following:

• 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 serious or life-threatening illness
• your computer or software failed just before or while you were preparing your online return
• service issues with HMRC 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 or mental illness you have
• you were unaware of or misunderstood your legal obligation
• you relied on someone else to send your return and they did not

You must send your tax return or payment as soon as possible after your reasonable excuse is resolved and you cannot blame a cheque being bounced or a failed payment for missing the deadline, or say you submitted it late because HMRC didn’t send you a reminder.

Anyone unable to pay their tax bill in full by the deadline can spread the cost using HMRC’s online ‘Time to Pay’ system, but you must file your Self Assessment tax return before setting this up.  

If you can’t pay your tax bill in full, or you owe less than £30,000 and are eligible, you can apply online without having to contact HMRC directly, while those that owe more than £30,000 can still apply but need to contact HMRC.

Myrtle Lloyd, HMRC’s Chief Customer Officer, said: “Millions of customers have already completed their tax returns and can start 2026 with one less thing to worry about.

“For anyone yet to file, don’t leave it until the last minute. Filing now means you know exactly what you owe and have time to arrange payment. Search ‘Self Assessment’ on GOV.UK to get started.”