Owe HMRC tax on old crypto gains? How to use the cryptoasset disclosure service

Perhaps you sold crypto for a profit a few years ago and didn’t realise it needed to go on a tax return. Perhaps you swapped one token for another, not knowing that counts as a disposal. HMRC has a dedicated route for putting this right: an online service to tell HMRC about unpaid tax on cryptoassets.

This guide explains who it’s for, how far back you need to go, what you’ll pay and how the process works.

Who should use it

HMRC’s service is for anyone who has identified unpaid tax on cryptoassets, such as exchange tokens like bitcoin, NFTs and utility tokens.

• For the current or previous tax year, HMRC says to declare income or gains on your Self Assessment return instead. See how to report crypto to HMRC.
• For earlier years, use the disclosure service.

HMRC warns that if you don’t come forward, you could be liable to additional interest and penalties.

Why it matters more now

HMRC will start receiving information about crypto users directly from platforms under the Cryptoasset Reporting Framework (CARF), with the first reports due in 2027. See the CARF and new exchange reporting. The penalty rules reward people who come forward before HMRC finds out.

How many years to go back

HMRC says the number of years depends on why the tax wasn’t paid:

What you’ll need to work out

Before you start, HMRC expects you to:

1. Collect information about the cryptoassets involved.
2. Work out how many years you need to declare.
3. Calculate the Capital Gains Tax and Income Tax you owe for each year.
4. Work out the interest, which is charged daily from when the tax was due until it’s paid. HMRC says it will reject a disclosure that doesn’t include the right interest. The late payment rate is the Bank of England base rate plus 4% (since 6 April 2025); it has been 7.75% since 9 January 2026, and earlier periods use the rates in force at the time, which HMRC publishes.
5. Work out any penalty.

HMRC lists the information you’ll need, including your National Insurance number, the number of transactions, the proceeds or income not declared, your acquisition costs and expenses, the gains or profits with calculations, the exchanges you used, and whether you used a commercial crypto tax calculator.

For how gains are calculated, including pooling and the same-day and 30-day rules, see UK crypto tax. For income such as staking or airdrops, see staking taxes.

Penalties: how they’re set

HMRC’s factsheet on penalties for inaccuracies sets out ranges based on your behaviour and whether the disclosure was unprompted (you told HMRC before you had reason to think it had found, or was about to find, the problem) or prompted:

The percentage is applied to what HMRC calls the potential lost revenue, broadly the extra tax that results from correcting the error. Within each range, HMRC reduces the penalty for the quality of your disclosure: up to 30% for telling, up to 40% for helping and up to 30% for giving access to records. It also considers how long you took to disclose.

A worked example

HMRC’s factsheet works through an example. A customer’s careless inaccuracy, which they hadn’t disclosed, is found in a check: a prompted disclosure, so the range is 15% to 30%. The potential lost revenue is £3,000, and HMRC gives a 70% reduction for the quality of disclosure:

1. Difference between maximum and minimum: 30% − 15% = 15 points.
2. Reduction: 15 × 70% = 10.5 points.
3. Penalty rate: 30% − 10.5% = 19.5%.
4. Penalty: £3,000 × 19.5% = £585.

Applying the same method to an unprompted disclosure, where the careless range is 0% to 30%, the same 70% reduction gives 30% − (30 × 70%) = 9%, or £270. With a full reduction, a careless unprompted penalty can be nil. That’s the reward for coming forward before HMRC contacts you.

Delay costs you

HMRC says that if you take a long time to disclose, for example 3 years or more, it will usually restrict the reduction for quality of disclosure to 10 percentage points above the minimum of the range. So the lowest penalties are only available to people who act promptly.

HMRC can also suspend a penalty for a careless inaccuracy for up to 2 years, with conditions to help you avoid future errors. If you meet them, the penalty isn’t paid. Penalties for deliberate behaviour can’t be suspended.

If you weren’t registered for Self Assessment at all, different failure to notify penalties may apply; HMRC’s guidance points to its factsheet on those too.

HMRC says it will consider whether the penalty you’ve applied is fair, and that there’s space on the form to explain. If it thinks your penalty is too low, it may carry out a further check.

Making the disclosure

1. Sign in to the online service (you can create sign-in details if you don’t have them).
2. Submit your disclosure: usually an offer to pay the full amount, including unpaid tax, interest and penalties.
3. Wait for a payment reference. HMRC says it will write with one; if you don’t hear within 15 working days, contact its helpline.
4. Pay within 30 days of submitting. If you can’t, contact HMRC to discuss options.
5. HMRC checks the disclosure and then writes to accept it or to ask for more information.

Practical tips

• Get your data first. Download full histories from every exchange and wallet, including closed accounts if possible.
• Don’t forget swaps and spending. Exchanging one crypto for another, or paying for things with crypto, are disposals.
• Include losses. They reduce your gains. GOV.UK says you can claim a loss up to 4 years after the end of the tax year in which you disposed of the asset.
• Consider an adviser for anything complicated, especially DeFi. See DeFi lending and staking tax.
• Beware of scams that pretend to be HMRC. HMRC says it will never threaten arrest. See government impersonation scams.