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HMRC Penalty & Voluntary Disclosure Calculator
Found unpaid tax? Answer a few questions to see the likely HMRC penalty, the interest, and how many years HMRC can look back, so you know what to expect before you come forward.
Step 1 · What happened
This is the biggest driver of the penalty. HMRC decides which applies, based on the facts, so pick the one you think HMRC would conclude.
Step 2 · How you come forward
Fully means telling HMRC everything, helping them work out the figures and giving access to your records.
Step 3 · The tax
The extra Income Tax, National Insurance or Capital Gains Tax, not the income. We spread it evenly across the years below.
How is this calculated?
Penalty. HMRC sets a minimum and a maximum percentage of the extra tax for each type of behaviour, depending on whether you tell HMRC before or after they contact you. The percentage that applies sits between the two, depending on how good your disclosure is: penalty % = maximum % minus (maximum % minus minimum %) multiplied by the quality of your disclosure. "Best case" uses the minimum, "worst case" the maximum, and "likely" uses the cooperation level you chose (full 100%, mostly 75%, partly 50%, limited 25%).
Time limit. HMRC can normally assess tax for 4 years after the end of the tax year, 6 years if the error was careless, and 20 years if it was deliberate or you failed to notify HMRC. Years outside the limit for the behaviour you select are left out of the figures.
Interest. Simple daily interest on each year's share of the tax, from 31 January after that tax year to today, using HMRC's published late payment rate for each period (currently 7.75% from 9 January 2026).
These figures are a general guide. They assume the tax is spread evenly over the years you pick and that you settle today, and they exclude offshore matters, VAT, Corporation Tax, late filing penalties, late payment penalties and interest on penalties.
How HMRC penalties for unpaid tax work
If you have underpaid tax, HMRC can charge a penalty on top of the tax and interest. The penalty is a percentage of the extra tax, and the percentage depends on your behaviour and on whether you tell HMRC first. Coming forward before HMRC contacts you is the single biggest way to reduce it.
| Behaviour | Before HMRC contacts you | After HMRC contacts you |
|---|---|---|
| Careless error in a return | 0% to 30% | 15% to 30% |
| Deliberate, not hidden | 20% to 70% | 35% to 70% |
| Deliberate and concealed | 30% to 100% | 50% to 100% |
Income you never told HMRC about follows the same ranges for deliberate behaviour. For careless cases the minimum is 0% (unprompted, within 12 months) or 10% (unprompted, later), and 10% or 20% if HMRC contacted you first.
Quick example: £10,000 of extra tax, careless, disclosed before HMRC contacts you with full cooperation, means a 0% penalty. The same £10,000 disclosed after HMRC contacts you, with partial cooperation, comes to about 22.5%, or £2,250.
Want the deeper read? See our guides: How to make a voluntary disclosure to HMRC, How far back can HMRC go and Code of Practice 9.
How HMRC classes your behaviour
| Category | What it means | Typical example |
|---|---|---|
| Honest mistake | You took reasonable care and still got it wrong. | Relying on a reasonable but mistaken reading of the rules. |
| Careless | You did not take reasonable care to get it right. | Forgetting to include a source of income or to check a figure. |
| Deliberate | You knew the return was wrong, or knew you should have told HMRC. | Leaving income out of a return on purpose. |
| Deliberate and concealed | As deliberate, plus steps taken to hide it. | Falsifying records or invoices to cover up the income. |
What happens when you make a disclosure
- Tell HMRC you want to disclose. This is normally done online through HMRC's disclosure service, which also gives you a reference number.
- Prepare the full figures. Work out the extra tax for each year, with supporting records. HMRC usually allows around 90 days from the notification to submit.
- Submit and pay. You send the disclosure and pay the tax, interest and penalty you have calculated.
- HMRC reviews. HMRC may accept the figures, ask questions, or open an enquiry before settling the final amounts.
How to keep the penalty down
- Come forward first. Telling HMRC before they contact you lowers the minimum penalty and shows the disclosure is genuine.
- Be complete. Disclose everything you know about, not just the part you think HMRC may find.
- Cooperate fully. Answer questions promptly and give access to records, because this is what earns the reduction inside the range.
- Get advice early. Mistakes in the disclosure itself can be treated as new errors.
If the amounts are large, or HMRC has already written to you, speak to our tax investigations team before you reply.
HMRC penalty calculator FAQs
What penalty can HMRC charge for unpaid tax?
It depends on why the tax went unpaid. For UK matters the penalty is a percentage of the extra tax: 0% to 30% if you were careless, 20% to 70% if it was deliberate but not hidden, and 30% to 100% if it was deliberate and hidden. Where exactly you land in each range depends on whether you came forward first and how well you cooperate. Offshore matters carry higher rates, up to 200%.
What is the difference between a prompted and an unprompted disclosure?
A disclosure is unprompted if you make it when you have no reason to believe HMRC has discovered, or is about to discover, the problem. Once HMRC has contacted you, opened a check or sent a letter about it, any disclosure is prompted. Prompted disclosures have higher minimum penalties: for example, 15% rather than 0% for a careless error.
How does HMRC pick a percentage inside the range?
It looks at the quality of your disclosure: how fully you tell HMRC what went wrong (telling), how much you help them work out the figures (helping) and whether you give them access to records (giving access). HMRC's guidance suggests weighting these 30%, 40% and 30%. The better the disclosure, the closer the penalty sits to the minimum. If a disclosure takes several years to come forward, HMRC will usually restrict the reduction it gives.
How far back can HMRC go?
Usually 4 years from the end of the tax year, extended to 6 years if the error was careless, and to 20 years if it was deliberate or you failed to tell HMRC about income you should have registered for. This calculator only counts the tax years inside the time limit for the behaviour you select.
Will I pay interest as well as a penalty?
Yes. HMRC charges late payment interest on unpaid tax from the date it was due (normally 31 January after the end of the tax year). The rate is the Bank of England base rate plus 4%, 7.75% from 9 January 2026, and it moves with the base rate. This calculator uses HMRC's published rate for each period, but your actual figure depends on your exact payment dates.
Should I use this calculator if HMRC has sent me a Code of Practice 9 letter?
No. A Code of Practice 9 letter means HMRC suspects deliberate behaviour and has opened a civil fraud investigation, with a strict deadline to respond. Speak to a specialist before replying. The figures here are a general guide and are not a substitute for advice on your own case.
How accurate is this HMRC penalty calculator?
It gives a range and a likely figure for UK (onshore) income tax, National Insurance and Capital Gains Tax. It assumes the unpaid tax is spread evenly across the years you pick and that you settle today. It does not include late filing or late payment penalties, offshore matters, VAT, Corporation Tax or interest on penalties, and HMRC alone decides the final penalty. Treat it as a planning guide.
What counts as careless?
Careless means you did not take reasonable care to get your tax right, for example by forgetting income, not keeping proper records or ignoring a figure you knew needed checking. HMRC treats it more leniently than a deliberate error.
Can HMRC charge a penalty if I tell them first?
Yes, but a disclosure made before HMRC contacts you can reduce the penalty to as low as 0% in careless cases. How complete and cooperative your disclosure is decides where the final figure falls.
Do I need to include every tax year?
You should disclose every year where tax is underpaid within HMRC's time limits. Leaving a year out and having HMRC find it later can push the penalty up and reduce the credit for cooperation.
Can I pay in instalments?
Often, yes. If you cannot pay in full, contact HMRC as soon as you can to agree a payment plan. Interest keeps running on the tax until it is paid.
Based on HMRC's published rules. See GOV.UK: Make a voluntary disclosure to HMRC, HMRC interest rates and the Compliance Handbook penalty tables.