HMRC Cryptoasset Disclosure Service: Step-by-Step Guide

HMRC's Cryptoasset Disclosure Service is the online route for telling HMRC about unpaid tax on crypto from earlier tax years and paying it, with interest and any penalty, in one go. You gather your records, work out the tax for each year, calculate interest and a penalty percentage, submit the disclosure through GOV.UK, and pay within 30 days of submitting. Anything for the current or previous tax year goes on your Self Assessment return instead — for 2025/26, that is the return due 31 January 2027.

This guide takes you through each step, using HMRC's own guidance. It covers how far back you need to go, how the penalty ranges work, and what happens after you submit. It is general information, not advice: if the sums are large, the behaviour could be seen as deliberate, or your situation is complicated, speak to a qualified adviser before you submit anything.

When should you use the Cryptoasset Disclosure Service?

Use it when you have identified unpaid Income Tax or Capital Gains Tax on cryptoassets — exchange tokens like bitcoin, NFTs or utility tokens — for a tax year that is now too old to include on a Self Assessment return. GOV.UK says: "If you need to declare any income or gains from the current or previous tax year, you will need to do this on your Self Assessment tax return."

So, in September 2026, gains or income for 2025/26 go on the return due 31 January 2027. If you are not in Self Assessment and only have a gain to report for 2025/26, you can also use HMRC's real time Capital Gains Tax service by 31 December 2026. Anything for 2024/25 or earlier that was never reported is a candidate for the disclosure service. If you filed a return for 2024/25 but left crypto off it, you can still amend that return until 31 January 2027.

If you want an agent to submit for you, you need to give them temporary authorisation to deal with your tax first.

Step 1: work out which years you need to disclose

The number of years depends on why the tax was not paid. GOV.UK sets out three categories, and you must decide which applies to you:

• You took reasonable care but still got it wrong — you pay what you owe for 4 years: the current year and the year before on your tax returns, plus the disclosure form for the 3 years before that.
• You did not take enough care — a maximum of 6 years: the current year and the year before on your returns, plus the 5 years before that on the disclosure form.
• You deliberately did not tell HMRC — a maximum of 20 years. GOV.UK defines deliberate as knowing you owed tax and choosing not to tell HMRC, or knowing the figures on your return were wrong when you submitted it.

Be honest with yourself here. Not knowing that a crypto-to-crypto swap was taxable is a common reason for under-reporting; whether that counts as reasonable care or carelessness depends on your circumstances, and HMRC will consider whether the penalty you have applied is fair. There is space on the form to explain your reasoning.

Step 2: gather your records

HMRC's disclosure form asks for a lot of detail, so collect everything before you start. GOV.UK lists what you will need:

• personal details: name, address, email address and phone number, plus your National Insurance number;
• the number of cryptoasset transactions;
• the amount of proceeds or income you have not declared, before deducting costs, and how many years it covers;
• the acquisition costs of the cryptoassets and any expenses;
• the amount of gains or profit you made, including your calculations;
• the exchanges you used and the number of cryptoassets disposed of;
• the tax and interest you owe, including calculations; and
• whether you used a cryptoasset commercial calculator, and which one.

In practice that means downloading the full transaction history from every exchange and wallet you used in the relevant years, plus bank statements showing deposits and withdrawals. HMRC's record-keeping guidance (CRYPTO10400) expects the type of token, date, buy or sell, number of units, sterling value at the time and your running balance for each transaction.

Step 3: calculate the Capital Gains Tax and Income Tax for each year

For each tax year, work out your gains and losses on every disposal using HMRC's pooling rules — same-day matching first, then the 30-day rule, then the section 104 pool — deduct the annual exempt amount for that year, and apply the rates that applied at the time. Add any staking, mining or lending income at its sterling value when received.

The allowances and rates have changed a lot, which is why year-by-year care matters:

Someone who made £10,000 of crypto gains in 2021/22 with no other gains owed nothing, because the allowance was £12,300. The same gains in 2024/25 would leave £7,000 taxable. Many people who never reported earlier years find that some of those years produce no tax at all — but you still need the calculation to show it.

GOV.UK's disclosure guidance acknowledges that "dealing with cryptoassets can be complicated" and says you can use a cryptoasset commercial calculator to help. Our calculator handles every tax year from 2019/20, applies the mid-year 2024/25 rate change, shows which matching rule applied to each disposal, and produces a disclosure worksheet you can keep as evidence. Your files are processed in your browser and never uploaded.

Step 4: work out the interest

Interest is charged daily from the date the tax was originally due until the date you pay. For Self Assessment years, tax was due on 31 January following the end of the tax year, so tax for 2022/23 has been accruing interest since 31 January 2024. GOV.UK is blunt: "If you do not include the right interest, we will reject your disclosure."

HMRC's late payment interest rate is set in legislation at Bank of England base rate plus 4% (from 6 April 2025; it was base rate plus 2.5% before that). The rate changes whenever the base rate moves, so use HMRC's published table of current and historic rates rather than a single figure, and work through each period separately. GOV.UK links to HMRC's penalties and interest calculator from the disclosure page, which does this for you once you have the tax figures.

Step 5: work out the penalty percentage

Penalties are a percentage of the tax you failed to pay ("potential lost revenue"). The percentage depends on your behaviour and on whether your disclosure is unprompted (you came forward before you had reason to think HMRC was about to find it) or prompted (any other time, including after a nudge letter). Within each range, the more you tell, help and give access to records, the lower the penalty.

HMRC's factsheet on inaccuracies in returns (CC/FS7a), which applies where you filed a return that left crypto out, gives these ranges:

If you never filed a return at all for a year in which you should have, the "failure to notify" factsheet (CC/FS11) applies instead. Its ranges for non-deliberate failures run from 0% to 30% (unprompted within 12 months of the tax being due) up to 20% to 30% (prompted, 12 months or more after), with the same 20% to 70% and 30% to 100% ranges for deliberate behaviour. HMRC will not charge a failure-to-notify penalty if you had a reasonable excuse and put things right without unreasonable delay once it ended.

Two practical points from the factsheets. First, if you take a long time — HMRC gives 3 years or more as an example — to make a disclosure, HMRC will usually restrict the reduction so you cannot reach the very bottom of the range. Second, HMRC can suspend a penalty for a careless inaccuracy for up to 2 years if it can set conditions to help you avoid future errors. The penalty is your proposal; HMRC checks it and may open a further check if it thinks the figure is too low.

Step 6: submit the disclosure and pay within 30 days

Sign in to the service through GOV.UK (you can create sign-in details if you do not have them), complete the form with your figures and explanations, and make your offer — normally the full amount of tax, interest and penalty. HMRC will write to you with a payment reference number. If you have not heard within 15 working days, call the helpline on 03000 55 22 94.

You must pay within 30 days of submitting your disclosure. If you cannot pay in that time, GOV.UK says to contact the helpline to discuss your options rather than simply missing the date. After checking your disclosure, HMRC will either write to accept your offer or contact you to say it cannot. It may ask you or your agent for evidence first, and if you do not provide it your offer might not be accepted. If HMRC finds you knowingly gave incorrect information, it may look at your affairs again and charge higher penalties.

What if you have left something out?

If you realise after submitting that you missed something, contact the helpline or write to HMRC at WMBC, HM Revenue and Customs, BX9 1BN. Correcting your own disclosure quickly is far better than HMRC finding the gap later.

What if you have received an HMRC crypto letter?

A nudge letter does not change the mechanics, but it does mean any disclosure is prompted, which raises the minimum penalty percentage. It also sets a response date, printed on the letter, that you should work to. Reply as the letter instructs even if your calculation shows nothing is owed, and keep the calculation as evidence.

Our letter helper asks a few questions — what you received, the deadline on it, which years you traded, whether you have filed before — and gives you a checklist with the right route for each year: Self Assessment, the real time service or the disclosure service.

Sources

• Tell HMRC about unpaid tax on cryptoassets — GOV.UK
• Compliance checks: penalties for inaccuracies in returns or documents — CC/FS7a — GOV.UK
• Compliance checks: penalties for failure to notify — CC/FS11 — GOV.UK
• HMRC interest rates for late and early payments — GOV.UK
• Check if you need to pay tax when you sell cryptoassets — GOV.UK
• Capital Gains Tax rates and allowances — GOV.UK
• Self Assessment tax returns: deadlines — GOV.UK
• Report and pay your Capital Gains Tax: other capital gains — GOV.UK
• Self Assessment tax returns: if you need to change your return — GOV.UK
• CRYPTO10400 — Record keeping — HMRC Cryptoassets Manual