Self Assessment Penalty Calculator | NoMoreJanuary
Free calculator for HMRC Self Assessment late filing penalties, late payment surcharges, and daily interest. See exactly what you owe in seconds.
Missed the 31 January deadline? Self Assessment has two separate penalty regimes that run independently: late filing (£100, then £10/day after 3 months, then £300 or 5% at 6 and 12 months) and late payment (5% surcharges at 30 days, 6 months, and 12 months, plus daily interest at 7.25%). You can be hit by one, both, or neither.
Enter your unpaid tax bill and how many days late you filed and/or paid. The calculator shows the full breakdown of every penalty and interest charge, with a grand total of what you owe.
Self Assessment Penalty Calculator
Enter how late you filed and/or paid, plus your unpaid tax bill, to see the full breakdown of HMRC penalties and interest.
You filed and paid on time — no penalties or interest. Tax due: £6,000.
Estimates based on HMRC's published penalty rules. Day counts are approximate (30 days ≈ 1 month, 183 ≈ 6 months, 365 = 12 months). Interest is simple, not compound. This tool does not cover the "failure to notify" regime for people who never registered for Self Assessment. Always verify against gov.uk.
How this calculator works
The calculator runs two independent penalty calculations and adds them together:
- Late filing: Triggers if you filed your return after 31 January. The £100 automatic penalty applies from day 1, even if you owe no tax. After 3 months (~91 days), £10/day is added (up to 90 days = £900 max). At 6 months and 12 months, a further £300 or 5% of tax due (whichever is higher) is charged.
- Late payment: Triggers if you paid your tax bill after 31 January and you owe tax. Daily interest accrues at 7.25% (the current HMRC late payment rate) from day 1. At 30 days, 6 months, and 12 months, a 5% surcharge on the unpaid tax is added — these are cumulative.
The two regimes run independently. You can file on time but pay late (only late payment charges apply), file late but pay on time (only late filing penalties apply), or both file and pay late (both apply).
The late filing penalty ladder
Late filing penalties escalate in four stages. The £100 is automatic and unavoidable — it applies even if you owe £0 or are due a refund:
| When | Penalty | Applies even if no tax owed? |
|---|---|---|
| 1 day late | £100 automatic | Yes |
| 3 months late (91 days) | £10/day for up to 90 days (max £900) | Yes |
| 6 months late (183 days) | £300 or 5% of tax due (whichever higher) | Yes (£300 minimum) |
| 12 months late (365 days) | £300 or 5% of tax due (whichever higher) | Yes (£300 minimum) |
If HMRC determines the failure to file was deliberate, the 12-month penalty rises to 100% of the tax due. This calculator does not cover the deliberate failure uplift — it assumes non-deliberate late filing.
The late payment penalty ladder
Late payment charges apply only if you owe tax and pay it late. They consist of daily interest plus three cumulative 5% surcharges:
| When | Charge | Based on |
|---|---|---|
| From day 1 | Daily interest at 7.25% | Unpaid tax × rate × days/365 |
| 30 days late | 5% surcharge | Unpaid tax |
| 6 months late (183 days) | 5% surcharge | Unpaid tax |
| 12 months late (365 days) | 5% surcharge | Unpaid tax |
The three 5% surcharges are cumulative — if you pay 12 months late, you face all three (15% total) plus the daily interest that has been accruing throughout. ATime to Pay arrangementsuspends the surcharges while you're on the plan, though interest continues to accrue.
Worked examples
1 day late, £3,000 tax bill, filed and paid late
Late filing: £100 automatic penalty. Late payment: £3,000 × 7.25% × 1/365 = £0.60 interest. No surcharges yet (first surcharge at 30 days).Total: £100.60 in penalties and interest, plus the original £3,000 tax bill = £3,100.60 grand total.
3 months late (91 days), £3,000 tax bill, filed and paid late
Late filing: £100 + £10/day × 1 day (day 91 is the first day of daily penalties) = £110. (Daily penalties run for up to 90 days from day 91, so at exactly 91 days late, only 1 day of daily penalties has accrued.) Late payment: £3,000 × 7.25% × 91/365 = £54.17 interest. No surcharges yet.Total: £164.17 in penalties and interest, plus £3,000 tax = £3,164.17 grand total.
6 months late (183 days), £3,000 tax bill, filed and paid late
Late filing: £100 + £10 × 90 days (max daily penalty) + £300 (6-month penalty, since £300 > 5% of £3,000 = £150) = £1,300. Late payment: £3,000 × 7.25% × 183/365 = £108.98 interest + £150 (5% surcharge at 30 days) + £150 (5% surcharge at 6 months) = £408.98.Total: £1,708.98 in penalties and interest, plus £3,000 tax = £4,708.98 grand total.
12 months late (365 days), £3,000 tax bill, filed and paid late
Late filing: £100 + £900 (90 days × £10) + £300 (6-month) + £300 (12-month) = £1,600. Late payment: £3,000 × 7.25% × 365/365 = £217.50 interest + £150 + £150 + £150 (three 5% surcharges) = £617.50.Total: £2,217.50 in penalties and interest, plus £3,000 tax = £5,217.50 grand total. That's 74% more than the original tax bill — all of it avoidable by filing and paying on time.
How to reduce or avoid these penalties
- File on time even if you can't pay. The £100 late filing penalty applies even if you owe £0. Filing on time avoids the entire late filing ladder, even if you can't pay the tax.
- Set up a Time to Pay arrangement. If you can't pay in full, a payment plan with HMRC suspends the 5% late payment surcharges. Interest still accrues, but at a much lower total cost. See our Time to Pay guide.
- Appeal if you have a reasonable excuse. HMRC may waive penalties if you had a valid reason for missing the deadline (bereavement, serious illness, HMRC system failure). See our guide on how to appeal an HMRC penalty.
- Pay as much as you can immediately. Interest is charged on the reducing balance, so partial payments reduce the total interest. Every pound paid early saves 7.25% annualised interest.
This calculator provides estimates based on current HMRC penalty rules and the 7.25% late payment interest rate as of early 2025. Interest rates can change. Your actual penalties may vary depending on your circumstances. Always refer toHMRC's official penalty guidance.
Frequently Asked Questions
How much is the penalty for filing a Self Assessment tax return late?
The initial penalty is £100, charged automatically the day after the 31 January deadline — even if you owe no tax. After 3 months, HMRC adds £10 per day (up to £900). At 6 months and 12 months, a further £300 or 5% of the tax due (whichever is higher) is charged.
What is the Self Assessment late payment surcharge?
HMRC charges 5% of the unpaid tax at 30 days, 6 months, and 12 months after the due date. These are cumulative — so if you pay 12 months late, you face all three 5% charges (15% total) plus daily interest. A Time to Pay arrangement suspends these surcharges.
Does the £100 late filing penalty apply if I owe no tax?
Yes. The £100 is automatic and applies even if you owe £0, are due a refund, or have no tax bill at all. The penalty is for failing to file, not for owing tax. If you're due a refund, HMRC usually offsets the penalty against it.
Does this calculator cover the failure to notify regime?
No. This calculator covers the late filing and late payment penalty ladders for people who were already registered for Self Assessment. If you never registered, a different regime ("failure to notify") applies where the penalty is based on unpaid tax — often £0 if you owed nothing. See our guide on not knowing you needed to register.