Millions of Brits have been urged to file their tax returns before a deadline this week or risk incurring a £100 penalty. Those who haven’t filed their online self-assessments for the 2024/25 year have been warned that failing to do so before 11:59pm on January 31 will mean receiving the initial penalty, rising by £10 a day after three months up to a maximum of £900. According to HMRC, around 3.3 million taxpayers may be yet to file ahead of the upcoming deadline.

Over a million people failed to file their tax returns on time last year, facing steep penalties as a result. Those who need to submit a self-assessment include people employed as “sole traders” who earned more than £1,000 between April 6, 2024 and April 5, 2025, those who were in a business partnership during that period and who paid Capital Gains Tax when they sold or disposed of something that increased in value.

The easiest way to pay any tax owed is via the free HMRC app, which takes under a minute.

Myrtle Lloyd, HMRC’s chief customer officer, said: “Don’t leave it until deadline day. Filing now will give you peace of mind that your tax return is completed and if you have tax to pay, you have a week to arrange payment.

“If you’re worried about paying your tax bill, you may be able to set up a payment plan online – search ‘difficulties paying HMRC’ on GOV.UK.”

8.6 million people had paid their tax return for the 2024 to 2025 tax year as of January 23, according to HMRC.

That’s compared to the 11.5 million who had filed ahead of the deadline this time last year.

After rising by £10 per day three months after failed payment, a further penalty of 5% of the tax or £300, whichever is greater, will be incurred after six months.

If 12 months elapses since the deadline with still no payment, taxpayers will be subject to yet another 5% or £300 charge.

“HMRC will consider customers’ reasons for missing the deadline,” official guidance reads. “Those with a reasonable excuse may avoid a penalty.”