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Self Assessment late penalty calculator

Estimate HMRC's penalties and interest if your Self Assessment tax return or payment is late: the £100 late filing penalty, daily penalties after 3 months, the 5% charges and late payment interest at 7.75%.

The penalties, as GOV.UK lists them

If you send your tax return late you get an initial £100 penalty. After 3 months, there are daily penalties of £10 a day, up to £900. After 6 months, a further penalty of 5% of the tax due or £300, whichever is greater, and after 12 months another 5% or £300. If you pay late, you get penalties of 5% of the tax unpaid at 30 days, 6 months and 12 months, and you are also charged interest on what you owe (GOV.UK).

Interest

HMRC's late payment interest rate is the Bank of England base rate plus 4%. It has been 7.75% since 9 January 2026 (HMRC interest rates). If the base rate changes, so does the interest rate, so treat the interest line as a guide.

Worked example

£2,000 of tax, with the return and payment both 200 days late: £100 + £900 of daily penalties + £300 (5% of £2,000 is only £100, so the £300 minimum applies) = £1,300 for filing late. Paying late adds 5% at 30 days and 5% at 6 months (£200), plus about £84.93 of interest. That's roughly £1,585 on top of the tax.

Deadlines for the 2025 to 2026 tax year

Paper returns by 11:59pm on 31 October 2026. Online returns and payment by 11:59pm on 31 January 2027. If you want the bill collected through your tax code, submit online by 30 December 2026 (GOV.UK).

Making Tax Digital changes the rules from 2026 to 2027

If you have to use Making Tax Digital for Income Tax from April 2026, new points-based late submission penalties and new late payment penalties apply from the tax year you join. The current penalties above still apply to your 2025 to 2026 return due on 31 January 2027 (GOV.UK). Check whether you're in with the Making Tax Digital checker.

Can't pay in full? GOV.UK says to contact HMRC about a payment plan. Plan ahead with the self-employed tax calculator and the payments on account calculator, or read how to register as self-employed.

Figures from GOV.UK, checked 17 October 2026. An estimate, not tax advice.

Questions

How much is the penalty for a late Self Assessment return?

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

How much interest does HMRC charge on late tax?

Base rate plus 4%. It has been 7.75% a year since 9 January 2026, according to HMRC's interest rates page.

Can I appeal a penalty?

Yes, if you have a reasonable excuse. You must pay a penalty within 30 days of the date on the notice. See GOV.UK.

Is there an official calculator?

Yes. GOV.UK has an estimate your penalty tool. Ours shows each step and the interest in one table.