Paying Self Assessment late: penalties and interest explained

Checked against GOV.UK on 23 October 2026. General information for sole traders in England, Wales and Northern Ireland, not tax advice. Scottish Income Tax rates are different.

The late payment penalties

GOV.UK says you'll be charged 5% of the tax still unpaid at each of these points after the deadline: 30 days, 6 months and 12 months. They're on top of any late filing penalty.

Interest

HMRC also charges interest from the day after the tax was due until it's paid. Since 6 April 2025 late payment interest has been the Bank of England base rate plus 4%. GOV.UK listed 7.75% from 9 January 2026 when we checked. The rate moves with the base rate, so check the HMRC interest rates page.

Worked example

Sam files on time but can't pay £3,000 due on 31 January 2027. He pays it all on 15 March 2027.

• At 30 days £3,000 is unpaid, so the penalty is 5% × £3,000 = £150.
• Interest on £3,000 for 43 days at 7.75% a year is about £3,000 × 7.75% × 43 ÷ 365 ≈ £27.

If he'd paid by the end of February, he'd only have paid interest.

If you can't pay in full

Don't ignore it. You can usually set up a payment plan online if you owe £30,000 or less and have filed your return. See Time to Pay explained. Pay what you can straight away, as penalties and interest are worked out on what's still unpaid.

Avoid it next year

Put a fixed share of every invoice aside. The self-employed tax calculator shows how much, and the January tax bill calculator shows what's due in January and July.

This guide is part of our Self Assessment guides for the self-employed.