HMRC Crypto Disclosure: How to Tell HMRC About Unpaid Tax

Headlines about an HMRC crypto crackdown can be unsettling, especially if you have traded crypto for a few years without reporting it. The reality is more measured. HMRC is gathering more data on crypto, it does write to people it thinks may owe tax, and it has a dedicated route for putting things right. If you have unpaid tax on crypto, an HMRC crypto disclosure made on your own initiative is usually the best way forward. This guide explains how the process works, what HMRC will want to know, and how interest and penalties are worked out.

The HMRC crypto crackdown: what is actually happening?

There is no single new law called a "crackdown". What has changed is the amount of information available to HMRC and how it uses it.

• Information from platforms. HMRC has statutory powers to obtain customer data from businesses and has used them with crypto platforms in the past.
• The Cryptoasset Reporting Framework (CARF). Since 1 January 2026, UK cryptoasset service providers have been collecting user and transaction data, with the first reports due to HMRC between 1 January and 31 May 2027. HMRC says the data will help it identify cryptoasset gains and income that have not been declared. Our article Do crypto exchanges report to HMRC? explains CARF in more detail.
• The cryptoasset section on tax returns. From 2024/25, Self Assessment returns include a dedicated cryptoasset section, making it easier for HMRC to see who has reported crypto and who has not.

For the UK crypto tax crackdown in 2026 and beyond, the practical effect is simple: unreported crypto activity is becoming easier for HMRC to spot.

HMRC crypto letters and nudge letters

HMRC uses "one to many" letters, sometimes called nudge letters, to contact groups of taxpayers it believes may need to check their tax affairs. Crypto holders have been the subject of several such campaigns, and published commentary indicates HMRC has been issuing a further wave of crypto letters between July 2026 and March 2027.

A nudge letter is not the same as a formal tax enquiry. It is usually a prompt to review your position and, if something is wrong, to put it right. That said, it should not be ignored. If you receive one:

1. Read it carefully and note any date by which HMRC asks you to respond.
2. Check whether your returns for the relevant years correctly reflect your crypto gains and income.
3. If everything is correct, keep your calculations and records in case HMRC asks for them.
4. If something is missing, take advice on the best way to correct it.

Be wary of unsolicited messages claiming to be from HMRC that ask for payment, passwords or wallet details. HMRC will never need your private keys or seed phrase.

How HMRC crypto disclosure works

GOV.UK's guidance, "Tell HMRC about unpaid tax on cryptoassets", explains how to make a voluntary disclosure if you owe tax on cryptoassets such as exchange tokens, NFTs and utility tokens. HMRC's press releases refer to this as the Crypto Disclosure Service. The process is online and you need to sign in, or create sign-in details, to submit it.

The main steps are:

1. Gather the information you need.
2. Calculate the tax, interest and penalties you owe.
3. Submit the disclosure online.
4. Receive a payment reference number from HMRC.
5. Pay within 30 days of submitting your disclosure.
6. HMRC reviews the disclosure and decides whether to accept your offer.

Disclosure is generally used for earlier years. If the issue relates to a recent return that can still be amended, correcting that return may be the more appropriate route. Which route applies depends on your circumstances.

What information you will need

According to GOV.UK, you will need:

• your personal details and National Insurance number
• the number of cryptoasset transactions
• the amount of proceeds or income you have not declared
• your acquisition costs and expenses
• which exchanges you used
• your tax calculations (GOV.UK notes a commercial calculator can be used)

How far back does a crypto disclosure go?

The number of years you need to include depends on why the tax was not paid. GOV.UK sets out:

Behaviour	Maximum years covered
You took reasonable care but still did not pay enough	4 years
You were careless (did not take reasonable care)	6 years
The error was deliberate	20 years

Deciding which category applies is an important judgement and should be backed by the facts. Many people simply did not realise that swapping one token for another, or receiving staking rewards, could be taxable. Whether that amounts to carelessness depends on the circumstances.

Interest and penalties on unpaid crypto tax

Interest

GOV.UK states that interest is charged daily from the date the tax was due until the date it is paid. Interest is not a penalty; it reflects the late payment, and it keeps running until the tax is settled.

Penalties

HMRC's factsheet on penalties for inaccuracies sets out ranges based on behaviour and whether the disclosure was prompted or unprompted:

Behaviour	Unprompted disclosure	Prompted disclosure
Reasonable care	No penalty	No penalty
Careless	0% to 30%	15% to 30%
Deliberate	20% to 70%	35% to 70%
Deliberate and concealed	30% to 100%	50% to 100%

Percentages are applied to the extra tax due. A disclosure is unprompted if you tell HMRC before it has discovered, or is about to discover, the inaccuracy. Within each range, HMRC reduces the penalty according to the quality of your disclosure: telling HMRC about the problem, helping HMRC work out the amount, and giving access to records. HMRC says it may reduce a penalty for a careless inaccuracy to nil only where the disclosure is unprompted.

Where you were not registered for Self Assessment and should have been, separate failure to notify penalty rules may apply. HMRC publishes a factsheet on those too.

Why getting your records organised first matters

The quality of a crypto disclosure depends on the quality of the numbers behind it. Before submitting anything, we would always recommend:

• Collecting complete histories from every exchange and wallet, including closed accounts and DeFi activity.
• Reconciling transfers between your own wallets so they are not treated as disposals.
• Applying the UK matching rules (same-day, 30-day and Section 104 pooling) to produce sterling gains for each tax year. See crypto Capital Gains Tax in the UK.
• Identifying income such as staking or lending rewards separately; see reporting staking and DeFi income.
• Including losses, which can reduce what you owe if they are claimed correctly. See crypto losses and tax in the UK.

Errors can work in either direction: overstated gains mean paying more than you owe, while understated gains may lead to further questions from HMRC. If you already have a report from crypto tax software, a review before you disclose can be worthwhile.

Frequently asked questions

Is there a mandatory HMRC crypto disclosure?

There is no separate "mandatory disclosure" scheme for crypto. However, if you owe tax on crypto you are required to pay it, and HMRC provides the "Tell HMRC about unpaid tax on cryptoassets" service for voluntary disclosures. Correcting your position before HMRC contacts you generally leads to lower penalties than waiting.

What should I do if I get an HMRC crypto letter?

Read it carefully, note any response date and check whether your past returns correctly include your crypto gains and income. If they do, keep your records and calculations. If something is missing, take advice on correcting it promptly. Do not ignore it, and never share passwords, private keys or seed phrases.

How many years do I need to disclose?

GOV.UK says up to 4 years if you took reasonable care, up to 6 years if you were careless, and up to 20 years if the underpayment was deliberate. Which category applies depends on the facts, so it is worth considering carefully and documenting your reasoning.

How long do I have to pay after disclosing?

After you submit your disclosure, HMRC writes to you with a payment reference number. GOV.UK says you must pay within 30 days of submitting your disclosure. Interest is charged daily from the original due date until payment, so delays increase the amount owed.

Will I definitely get a penalty?

Not necessarily. There is no penalty where you took reasonable care. For careless errors disclosed unprompted, HMRC can reduce the penalty to nil. Deliberate behaviour carries higher minimum penalties. The final figure depends on your behaviour and on how fully you tell, help and give HMRC access to records.

Putting your crypto tax right

An HMRC crypto disclosure does not need to be a frightening process. With organised records, accurate calculations and a clear explanation, most people can resolve past issues and move forward with confidence. If you would like help preparing a disclosure, reviewing your records or responding to an HMRC letter, please get in touch for a confidential conversation. You can also read more about our crypto tax return and DeFi, staking and NFT services.