HMRC has handed out instant £100 fines to an estimated 1 million UK households this week after they all missed its deadline for self-assessment tax returns.

Every year, millions of people are liable to submit a tax return to HM Revenue and Customs for various reasons, such as being self-employed, earning income on the side, earning too much savings income or having to pay the Child Benefit High Income charge.

But HMRC has today revealed that roughly one million people have missed the January 31 deadline to submit and pay their return and will be hit with automatic £100 fines unless they can plead their case successfully to overturn it.

Those who failed to pay on time will also be made to pay interest on any outstanding money they owe as well as the £100 fine, which is given out automatically to anyone missing the deadline for any amount.

According to the figures, released by HM Revenue and Customs (HMRC), 11,489,825 returns were received by the deadline on January 31.

This includes returns that were expected, voluntary returns and late registrations.

The revenue body estimated that around one million customers missed the deadline.

It said that figures are indicative and there may be further adjustments once all figures have been ratified.

Charlene Young, a senior pensions and savings expert at AJ Bell, said: “An estimated one million people failing to file could net HMRC £100 million in automatic fees alone.

“There is an automatic £100 fine for late filing.”

HMRC said that, among those who filed their 2024-25 return to beat the deadline, 475,722 taxpayers waited until the final day on Saturday to file their return.

This included 27,456 people who submitted returns between 11pm and 11.59pm, in the final minutes before the deadline at the end of the day.

The busiest hour on the day for submitting a return was 5pm to 5.59pm, when 32,982 people filed.

HMRC advisers handled 5,409 webchats and 10,483 calls to its helplines on the day.

HMRC had been due to keep its phone lines closed on deadline day, but pulled a U-turn following reporting by the Express.

People may be able to avoid a penalty if they have a reasonable excuse for filing late.

Time to pay arrangements are available for those who cannot pay their tax bill in full, if they meet the relevant criteria.

Ms Young said: “If you don’t have an excuse to appeal a fine but still owe money, you might still be able to set up a payment plan to get back on track.

“It’s essential you don’t put your head in the sand.”

Myrtle Lloyd, HMRC’s chief customer officer, said: “Thank you to the millions of people and agents who filed their self-assessment tax return and paid any tax owed by January 31.

“Anyone who missed the deadline should file their return as soon as possible, as penalties and late payment interest may be charged.”

People will be able to file their self-assessment tax return for the 2025-26 tax year from April 6, 2026.