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If you miss the 31st January deadline, HMRC will start charging you interest immediately (from 1st February) on any unpaid tax.

• If you pay within 30 days: You will only be charged interest.
• If you pay more than 30 days late: You will be charged interest plus a penalty fee of 5% of the tax you owe.
• If you haven’t filed your return yet: You will also get an automatic £100 fine just for filing late, even if you don’t owe any tax.

Do not ignore it. If you cannot pay, contact HMRC immediately to set up a “Time to Pay” plan. This stops the penalty fees, though interest will still build up.

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Missed the 31st January Deadline? Here is What Happens Next

For millions of people in the UK, the 31st of January is the most important date in the calendar. It is the deadline to file your online Self Assessment tax return and pay any tax you owe for the previous tax year.

If you have missed this date, don’t panic—but you must act quickly. Ignoring the problem will make it much more expensive.

1. You will be charged interest immediately

From the very next day (1st February), HMRC charges interest on any unpaid tax.

• The rate: As of early 2026, the late payment interest rate is 7.75%.
• How it works: This is an annual rate, but it is calculated daily. This means the sooner you pay, the less interest you will be charged.

2. The Late Payment Penalties

If you leave the bill unpaid, HMRC adds extra fines on top of the interest. These are called “late payment penalties.”

How late is the payment?	The Penalty
30 days late	5% of the tax you still owe.
6 months late	An additional 5% of the tax you still owe.
12 months late	A final 5% of the tax you still owe.

Example:

If you owe £1,000 and pay nothing for a month, you will owe the original £1,000 + interest + a £50 penalty.

3. Did you file your return on time?

There is a difference between filing (sending the form) and paying (sending the money).

• If you didn’t file the form by 31st Jan: You get an instant £100 fine. This applies even if you have no tax to pay or have already paid it.
• If you filed but didn’t pay: You avoid the £100 fine, but the interest and payment penalties listed above still apply.

What to do if you can’t afford to pay

HMRC is usually reasonable if you communicate with them before problems get worse. If you cannot pay the full amount, you can ask for a “Time to Pay” arrangement.

This lets you spread your tax bill over monthly instalments (usually up to 12 months).

You can often set this up online if:

• You have filed your latest tax return.
• You owe less than £30,000.
• You are within 60 days of the payment deadline.
• You plan to pay off your debt within the next 12 months.

If you set this up:

• Good news: You avoid the 5% late payment penalties.
• Bad news: You still have to pay the interest (7.75%) on the money you owe until it is cleared.

Summary Checklist

1. File your return immediately if you haven’t done so (to stop the filing fines growing).
2. Pay as much as you can now to reduce the interest charges.
3. Go to GOV.UK and search for “Time to Pay” to set up a monthly payment plan for the rest.

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