One million MISS self assessment tax deadline – what can you do?

One million customers missed the self assessment tax deadline on 31 January 2026, according to the latest data from HM Revenue and Customs (HMRC).

Over 12 million customers were expected to file a tax return and pay any tax owed for the 2024-25 tax year by 31 January.

Just under 11.5 million people filed in time for the deadline, with 475,722 taxpayers waiting until the day to submit.

What happens if you miss the deadline?

If you miss the self assessment deadline, you might face the following penalties:

• initially: a £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’s also an additional late penalty of which is 5% of the unpaid tax at 30 days, 6 months and 12 months. You’ll also have to pay interest on any tax paid late.

What should you do if you miss the deadline?

It’s important to act quickly if you have missed the self assessment tax deadline to reduce penalties and late charges.

You must pay the penalty within 30 days of the date on the penalty notice. Otherwise, you’ll be charged interest.

One of the quickest ways to settle your tax bill is online through your tax account. You might be able to set up a payment plan to cover your overdue tax in monthly installments.

If you run into trouble, you can contact HMRC via telephone on 0300 200 3854 or by post using the address HMRC, DMB 601, BX9 1JH, United Kingdom.

Can you appeal the charges?

It’s possible to appeal against penalties issued by HMRC either online or via post using an SA370 or SA371 form.

You’ll need to have the following details ready to share:

• the date the penalty was issued
• the date you filed your Self Assessment tax return (if you have submitted it)
• the date you paid your tax (if you have paid it)
• details of your reasonable excuse for filing your return late, or not making your payment on time

Even if you do appeal, it’s still worth paying the penalty. That’s because if your claim is rejected, you’ll have to pay interest on the penalty from the date it was due to the date you paid it.

If HMRC agrees with your appeal, they’ll repay you with interest from the date you paid it. So long as you don’t have any other outstanding tax to pay.

When can you file your next tax return?

You’ll be able to file a self assessment tax return for the 2025 to 2026 tax year from 6 April 2026.