HMRC Late Filing Penalty Calculator
Enter how late your Self Assessment return is and your estimated tax bill. We calculate your exact penalty charges plus HMRC interest — updated for 2025/26 rates.
Not sure? Use your best estimate — you can amend the return later. Penalties still apply on nil returns.
Daily charges are running. The 6-month surcharge adds £300 in 93 days.
Total estimated exposure
£192
Penalties (£100) + interest (£92)
Full breakdown
Total penalties
£100
Interest on tax
£92
Tax owed
£5,000
Grand total
£5,192
What filing TODAY saves vs. waiting
HMRC Interest Calculator 2025/26
The calculator above functions as a full HMRC interest calculator for the 2025/26 tax year. HMRC charges late payment interest at the Bank of England base rate plus 4 percentage points — currently 8.25% annually. Interest accrues daily from the original payment deadline (31 January following the tax year end) until the day the balance is cleared, so every day you delay adds to the total you owe.
Unlike the fixed late filing penalties (£100, then daily charges, then 5% surcharges), interest is not capped and continues to grow indefinitely on any unpaid tax. It is also not subject to the same appeal grounds as penalties — HMRC will almost never cancel interest even where a reasonable excuse is accepted for the late filing itself. This is why paying the tax owed, even an estimate, is usually the single most effective action you can take to stop the meter running.
To estimate your own interest, enter your tax owed and days late into the tool at the top of this page. The result updates in real time and uses the current HMRC rate.
Estimated Tax Penalty Calculator 2025
This tool also works as an estimated tax penalty calculator for 2025 Self Assessment deadlines. Even if you do not yet know your exact tax liability, you can enter a conservative estimate and see what your total exposure looks like. HMRC penalties are calculated on the tax owed, so a realistic estimate gives you a realistic worst-case figure to plan against.
If you are unsure of the amount, use your previous year’s tax bill as a starting point and add 10-15% to be safe. Our accountants can refine this figure once we have sight of your records.