What happens the day after the deadline
If your 2025/26 return is not filed by midnight on 31 January 2027, HMRC charges a fixed £100 late filing penalty. It applies even if you owe no tax, or if you have already paid. For the first three months, nothing else is added for filing late — so the best thing you can do is file as soon as you can.
Paying late is a separate matter. From 1 February 2027, HMRC charges interest on any unpaid tax at 7.75% a year (the Bank of England base rate plus 4%). Interest is small per day, but it keeps running until you pay.
Example: £1,500 of tax, filed and paid in February
The calculator above is set for a return filed in February 2027 with £1,500 to pay, paid on 20 February 2027 (20 days late):
- Late filing penalty: £100
- Interest: £1,500 × 7.75% × 20 ÷ 365 = £6.37 (about 32p a day)
- Total extra cost: £106.37, so £1,606.37 to HMRC altogether
The date that really matters: 2 March 2027
If tax is still unpaid 30 days after the deadline, HMRC adds a 5% late payment penalty. Paying by 2 March 2027 avoids it. On £1,500, waiting even one more day adds £75:
| Days late paying £1,500 (return filed in February) | Penalties + interest |
|---|---|
| 0 (paid 31 January) | £100.00 |
| 20 | £106.37 |
| 30 | £109.55 |
| 31 | £184.87 |
| 60 | £194.11 |
| 90 | £203.66 |
Your calm to-do list
- File online now. Even if some figures are estimates, you can amend the return later (you have 12 months from the deadline).
- Pay what you can, as soon as you can. Every payment reduces the interest.
- Can’t pay it all? If you owe £30,000 or less and have filed, you may be able to set up a Time to Pay plan online. A plan agreed before the 30-day point stops the 5% penalty, although interest still applies.
- Had a good reason? If something serious stopped you — illness, a bereavement, a system failure — you can appeal the £100 with a “reasonable excuse”. Appeal within 30 days of the date on the penalty notice.
The current penalty rules still apply to 2025/26 returns, including for people who joined Making Tax Digital for Income Tax in April 2026. The interest rate can change when the Bank of England moves base rate — you can type a different rate into the calculator.
FAQ
I missed the deadline by a few days. What do I owe?
A £100 late filing penalty plus interest on any unpaid tax. With £1,500 paid 20 days late, that is £100 + £6.37 interest = £106.37.
How much interest does HMRC charge per day?
7.75% a year. On £1,500 that is about 32p a day — £6.37 for 20 days.
How do I avoid the 5% late payment penalty?
Pay in full by 2 March 2027 (30 days after the deadline), or agree a Time to Pay plan before then. On £1,500, the penalty would be £75.
Sources (checked 5 November 2026): GOV.UK “Self Assessment tax returns: penalties” (gov.uk/self-assessment-tax-returns/penalties); GOV.UK “Penalties for Making Tax Digital for Income Tax” (current penalties apply to the 2025 to 2026 return due 31 January 2027); GOV.UK “HMRC interest rates for late and early payments” (7.75% from 9 January 2026); Finance Act 2009 Schedules 55 and 56; ICAS “Self-assessment penalties: which regime applies for 2025-26 and 2026-27”.