Estimate Your HMRC Penalties
Use this tool to estimate standard Self Assessment late filing penalties, late payment penalties, and simple interest.
This calculator is an educational estimate based on standard Self Assessment rules (fixed £100, daily penalties after 3 months, and additional penalties after 6 and 12 months, plus 5% late payment stages). It does not include special or deliberate behaviour penalties.
How this HMRC penalty calculator works
If your Self Assessment tax return is filed late, or your tax bill is paid late, HMRC can apply separate charges. Many people are surprised that filing penalties and payment penalties can both apply at the same time. This calculator helps you model that combined impact so you can plan cash flow and act quickly.
The estimate shown here has three parts:
- Late filing penalties (based on how late your return is sent)
- Late payment penalties (based on how late your tax is paid)
- Interest on unpaid tax (calculated using a simple annual interest estimate)
Penalty rules used in this estimate
1) Late filing (Self Assessment)
- 1 day late: fixed penalty of £100
- More than 3 months late: £10 per day, up to 90 days (max £900)
- More than 6 months late: extra penalty of £300 or 5% of tax due (whichever is higher)
- More than 12 months late: another £300 or 5% of tax due (whichever is higher)
2) Late payment (standard staged model)
- More than 30 days late: 5% of unpaid tax
- More than 6 months late: additional 5% of unpaid tax
- More than 12 months late: additional 5% of unpaid tax
3) Interest
Interest is estimated as: tax owed × (annual rate ÷ 100) × (days late ÷ 365). HMRC interest rates change over time, so you can update the percentage input to reflect the current figure.
Example calculation
Suppose your tax owed is £4,000, your return is 120 days late, and payment is 75 days late.
- Filing: £100 fixed + £300 daily penalties (30 days at £10/day after 90 days) = £400
- Payment: 5% after 30 days = £200
- Interest: estimated based on days late and the selected annual rate
Your total cost becomes: tax due + penalties + interest. The key takeaway is simple: every extra week can increase what you owe.
How to reduce or avoid HMRC penalties
File first, even if you cannot pay in full
Filing late triggers automatic penalties quickly. If possible, submit the return on time even when payment is difficult. You may still face late payment charges, but you can often avoid the largest filing penalties.
Set up a payment plan quickly
HMRC may allow a Time to Pay arrangement depending on your circumstances. Contacting HMRC early can reduce escalation risk and show proactive intent.
Keep evidence if you had a reasonable excuse
In some cases, penalties can be appealed where a valid reasonable excuse existed (for example, serious illness or major service disruption). Keep dates, records, and supporting documents.
Important notes and limitations
- This page provides a practical estimate, not formal tax advice.
- HMRC rules can differ by tax type and can change over time.
- Some cases involve additional penalties not included here (for example, deliberate withholding scenarios).
- If your numbers are substantial, consider speaking with a qualified accountant or tax adviser.
Quick FAQ
Do I still get a filing penalty if no tax is due?
The initial fixed filing penalty can still apply even if no tax is payable.
Can HMRC penalties be appealed?
Yes, in certain circumstances. Appeals usually require a clear explanation and supporting evidence.
Does paying part of the tax help?
Yes. Reducing the unpaid balance can lower percentage-based penalties and interest over time.