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Self Assessment Penalty & Interest Calculator

See how much HMRC adds when a Self Assessment return is filed late or tax is paid late, every late filing and late payment penalty, plus daily interest at the published rates.

In short: What is the penalty for filing a Self Assessment return late?

£100 straight away. After 3 months, £10 a day for up to 90 days (£900). After 6 months, a further 5% of the tax due or £300, whichever is greater, and the same again after 12 months.

Last reviewed against 2 official sources.

Try an example:

Your tax return

When you filed and paid

Penalties are worked out to today if you haven't yet

Penalties and interest

£2,149.70

on top of the £6,000.00 tax

Initial late filing penalty
£100.00
Daily penalties (90 days × £10)
£900.00
6-month penalty (5% or £300)
£300.00
Late payment penalty at 30 days (5%)
£300.00
Late payment penalty at 6 months (5%)
£300.00
Late payment interest (196 days)
£249.70

If you had a reasonable excuse for filing or paying late, you can ask HMRC to cancel a penalty. Check HMRC's guidance on appealing a penalty.

What makes up the total

Penalties and interest add £2,149.70 to £6,000.00 of tax.

When each penalty is added

HMRC adds penalties at fixed points after the 31 January deadline.

The link holds your numbers in the address. Nothing is sent to us.

The penalty timetable

WhenLate filingLate payment
Day after the deadline£100Interest starts
30 days 5% of unpaid tax
3 months£10 a day, up to £900 
6 months5% of tax due or £3005% of unpaid tax
12 months5% of tax due or £3005% of unpaid tax

Worked example

Ali owes £6,000 for 2024-25 and files and pays on 15 August 2026, six and a half months after the 31 January deadline. Filing penalties: £100 + £900 daily + £300 = £1,300. Payment penalties: two 5% charges = £600. Interest for 196 days at 7.75% ≈ £250. Total: about £2,150 on top of the tax.

Limits

  • Interest is simple and on the unpaid tax only; partial payments reduce it.
  • The 12-month penalty can be higher if HMRC finds information was withheld deliberately.
  • Payments on account and their interest aren't included.

Reading the charts

Each chart redraws as you change the inputs and uses the same calculation as the result above. Choose "Show data" for the exact figures as a table, or download them as a CSV. "Copy link" saves your numbers in the page address so you can come back to the result or share it; nothing is sent to us.

Official sources

Figures last reviewed .

Frequently asked questions

What is the penalty for filing a Self Assessment return late?

£100 straight away. After 3 months, £10 a day for up to 90 days (£900). After 6 months, a further 5% of the tax due or £300, whichever is greater, and the same again after 12 months.

What is the penalty for paying late?

5% of the tax still unpaid at 30 days, again at 6 months and again at 12 months, plus interest on the amount owed.

Do I get a penalty if I owe no tax?

Yes for filing late. The £100 and daily penalties apply even if there's no tax to pay. Late payment penalties and interest only apply to unpaid tax.

What interest rate does HMRC charge?

Late payment interest is the Bank of England base rate plus 4%. It has been 7.75% since 9 January 2026. The calculator uses each period's rate.

Can I appeal?

If you had a reasonable excuse for filing or paying late you can ask HMRC to cancel a penalty; HMRC decides each case. File and pay as soon as you can either way, because penalties and interest keep building.

When do I have to pay a penalty?

Within 30 days of the date on the penalty notice.

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Disclaimer: This tool gives a general estimate based on what you enter and the published rules. It is not tax, legal or financial advice, and the tax authority makes the final decision. Speak to a qualified professional before acting. See our disclaimer.