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Work out roughly what you could owe HMRC on undeclared income or gains. Add each tax year, choose today’s date or the date you plan to pay, and the calculator applies HMRC tax rates, late payment interest and penalty ranges. Download your results as a PDF or CSV.
Fully registered and compliant to act on your behalf.
Add a row for each tax year with undeclared income or gains. Then press Calculate.
Add each tax year you need to disclose. Figures are estimates using HMRC rates for England, Wales and Northern Ireland. Scottish taxpayers, dividends, savings and gains: choose “I will enter the tax”.
This calculator gives an estimate only and is not HMRC’s official calculator. It uses HMRC late payment interest rates from GOV.UK, charged daily from 31 January after each tax year, personal allowances, tax bands and Class 4 National Insurance for each year, and HMRC’s standard penalty ranges. Class 4 is worked out on the undeclared profit on its own. It does not include Class 2 National Insurance, payments on account, Scottish or Welsh rate differences, or other reliefs. Check the figures with an accountant before submitting a disclosure.
The calculator follows the same steps HMRC uses when it works out what is owed on a disclosure.
Income Tax is worked out using the personal allowance and tax bands for each year, including the allowance taper over £100,000. Self-employed profits also get Class 4 National Insurance. Gains use the Capital Gains Tax rates and annual exempt amount for that year.
Interest runs daily from 31 January after the end of each tax year until the date you choose. It uses each HMRC late payment interest rate for the days it applied. Interest is not a penalty and cannot be reduced.
The penalty depends on why the tax was missed, whether you came forward before HMRC contacted you, and whether the income was offshore. Better disclosure brings the penalty down towards the minimum.
HMRC can usually go back 4 years, 6 years for careless errors and up to 20 years for deliberate behaviour or offshore matters. The calculator flags years that may be outside these limits.
These are the rates HMRC charges on late Income Tax, National Insurance and Capital Gains Tax. The calculator uses all of them, day by day.
| Rate applies from | Late payment interest rate |
|---|---|
| 24 November 2026 | 8.00% |
| 9 January 2026 | 7.75% |
| 27 August 2025 | 8.00% |
| 28 May 2025 | 8.25% |
| 6 April 2025 | 8.50% |
| 25 February 2025 | 7.00% |
| 26 November 2024 | 7.25% |
| 20 August 2024 | 7.50% |
| 22 August 2023 | 7.75% |
| 11 July 2023 | 7.50% |
| 31 May 2023 | 7.00% |
| 13 April 2023 | 6.75% |
| 21 February 2023 | 6.50% |
| 6 January 2023 | 6.00% |
| 22 November 2022 | 5.50% |
| 11 October 2022 | 4.75% |
| 23 August 2022 | 4.25% |
| 5 July 2022 | 3.75% |
| 24 May 2022 | 3.50% |
| 5 April 2022 | 3.25% |
| 21 February 2022 | 3.00% |
| 7 January 2022 | 2.75% |
| 7 April 2020 | 2.60% |
| 30 March 2020 | 2.75% |
| 21 August 2018 | 3.25% |
| 21 November 2017 | 3.00% |
| 23 August 2016 | 2.75% |
| 29 September 2009 | 3.00% |
Source: HMRC interest rates for late and early payments, GOV.UK. Since 6 April 2025 the rate is Bank of England base rate plus 4%. The 8.00% rate from 24 November 2026 is already used by the calculator for days after that date.
The calculator uses these standard ranges from HMRC’s penalty factsheets.
| Behaviour | Unprompted | Prompted | Maximum |
|---|---|---|---|
| Reasonable care | No penalty | No penalty | 0% |
| Careless | 0% to 30% | 15% to 30% | 30% |
| Deliberate | 20% to 70% | 35% to 70% | 70% |
| Deliberate and concealed | 30% to 100% | 50% to 100% | 100% |
For offshore matters the ranges are higher. In category 2 territories they are 1.5 times the UK figures, and in category 3 territories they are doubled, up to 200%. Some offshore penalties can be higher still. If you take more than 3 years to come forward, HMRC may limit the reduction so the penalty is at least 10 percentage points above the minimum.
Prompted means HMRC had already contacted you, or you had reason to believe it was about to find the problem. Read more in our guide to HMRC disclosure penalties and interest.
Use our guides to choose the right route, then contact us so we can check your figures.
Our earlier articles on voluntary disclosures, the Worldwide Disclosure Facility, COP9, offshore income and HMRC enquiries.
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Wingate Accountants Ltd is an independent firm of Chartered Certified Accountants, providing tax and compliance services to individuals and businesses across the UK.
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