How to use the Self Assessment penalty calculator
- 1 Enter the tax due on the return.
- 2 Enter how many days late the return is (0 if it was filed on time).
- 3 Enter how many days the tax has been unpaid after the 31 January deadline.
- 4 Check the interest rate, which is Bank Rate plus 4%, then read the total.
Worked example
£2,500 of tax due, with the return filed and the tax paid 120 days late. Late filing costs £100 plus 30 days of £10 daily penalties, so £400. Late payment adds 5% at 30 days, which is £125. Interest at 8% for 120 days is £65.75, making £590.75 on top of the tax.
Limiting penalties
- File even if you cannot pay: filing stops the filing penalties growing.
- Pay what you can: interest and payment penalties apply only to what is unpaid.
- Set up Time to Pay before the 30-day point.
- Appeal within 30 days if you have a reasonable excuse.
Plan next year's payments with the Payments on Account Calculator and check whether MTD applies with the Making Tax Digital Checker.
Features
Filing and payment penalties
Every stage of both penalty schedules.
Interest included
Daily interest at the rate you enter, 8% by default (from 24 November 2026).
Clear breakdown
Shows each penalty and the total owed with the tax.
When to use it
Missed the 31 January deadline
See what you owe now and what is coming if you wait longer. For the tax itself, use the Self-Employed Tax Calculator.
Can't pay in full
See how penalties grow, then set up a Time to Pay plan with HMRC.
Payments on account
Plan July and January payments with the Payments on Account Calculator.
Moving to Making Tax Digital
Check when MTD applies with the Making Tax Digital Checker.
Related Tax tasks
Frequently asked questions
What is the penalty for a late tax return?
£100 as soon as the return is late, even if no tax is owed. After 3 months, £10 a day for up to 90 days (£900). After 6 months, 5% of the tax due or £300, whichever is more, and the same again after 12 months.
What is the penalty for paying tax late?
5% of the tax still unpaid at 30 days, another 5% at 6 months and another 5% at 12 months, on top of interest.
What interest does HMRC charge?
Bank of England Bank Rate plus 4 percentage points, charged daily from the day after the deadline. Bank Rate rose to 4% on 5 November 2026, so the rate is 8% from 24 November 2026 (7.75% before that). The rate changes when Bank Rate changes, so you can enter a different figure.
When is the Self Assessment deadline?
31 January after the end of the tax year for online returns and payment. For the 2025/26 tax year, that is 31 January 2027. Paper returns are due by 31 October.
Can I appeal a penalty?
Yes, if you have a reasonable excuse, such as serious illness, a bereavement or an HMRC system failure. Appeal within 30 days of the penalty notice.
Do penalties apply if I owe no tax?
Late filing penalties do. The £100 and daily penalties apply even when no tax is due, although the 6 and 12 month penalties are then £300 each.
Are penalties different under Making Tax Digital?
Yes. For people in Making Tax Digital from 2026/27, late submissions earn points instead of fixed fines, and late payment penalties work differently. This calculator covers returns outside MTD, such as 2025/26 returns.
Can I set up a payment plan?
Yes. If you owe £30,000 or less you can usually set up a Time to Pay arrangement online, which stops further late payment penalties if agreed in time, although interest still runs.
Is the calculation exact?
It is a close estimate. HMRC works out penalties on the tax due at each date, so payments made along the way reduce later penalties and interest.
Results are estimates based on the official rates linked above. Confirm important figures with the issuing authority or a qualified adviser before you act on them.
Built and reviewed by Hamza Farooq, founder and lead developer
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