Received an HMRC Letter About Crypto? What to Do

What the letter is

HMRC sends what it calls "one to many" letters: the same letter, sent to a large group of people at once. The crypto version goes to people HMRC's records suggest have disposed of cryptoassets, where it looks as if the gains or income may not have been fully reported. Figures published by accountancy group UHY Hacker Young put the number at about 65,000 in 2024/25 and about 81,000 in 2025/26 (Accountancy Age).

A new round is under way. ICAEW reports that between July 2026 and March 2027, HMRC's Wealthy and Mid-sized Business Compliance team will contact people it believes may have underpaid income tax or capital gains tax on crypto, by letter, email or text (ICAEW, 23 July 2026). If you have a tax agent, they get a copy.

What it asks you to do

The 2024 letter, published by the Chartered Institute of Taxation (CIOT), explains that selling crypto, swapping one token for another, spending it and giving it away are all disposals, and that staking, lending and mining can create income. It then sets out three options: amend your Self Assessment return if you are still in time, report older years through the cryptoasset disclosure service, or contact HMRC with information showing why you have no tax to pay. It asked for this within 60 days of the date of the letter.

The 2026 letters, as ICAEW summarises them, make the same points: amend the return, or use the disclosure service if it is too late to amend, and no action is needed if you have no income or gains to report. Your letter is the one that counts, so read its deadline and the tax years it mentions.

The certificate of tax position

Some HMRC campaign letters come with a form called a "certificate of tax position", asking you to declare that your tax affairs are in order. CIOT guidance on HMRC's letters about overseas income, which come with this certificate, says there is no legal obligation to complete it, and that HMRC has said it will accept a reply by letter instead (CIOT). Whatever you send, only confirm figures you have checked.

If you ignore it

Ignoring the letter does not make any tax go away. The 2024 letter says HMRC may raise an assessment for tax it thinks is due, will charge interest on tax paid late, and will consider penalties case by case. CIOT guidance on HMRC's similar letters about overseas income adds that HMRC follows up people who do not respond, first with another letter, and may then decide on further steps such as a phone call or an enquiry. Replying, even to say nothing is owed, is usually the simpler path.

Why HMRC will know more from 2027

Under the Cryptoasset Reporting Framework, UK crypto platforms collect their users' details and report them to HMRC with a summary of each user's transactions. The first reports cover 1 January to 31 December 2026 and are due between 1 January and 31 May 2027 (GOV.UK). HMRC says it uses this to link your crypto activity to your tax record, and a user who gives a platform inaccurate details or none can be charged up to £300 (GOV.UK).

What to do now

1. Read the letter carefully. Note the reference number, the reply date, the tax years it mentions and whether a certificate is enclosed. HMRC's phone line cannot correct your return or work out your tax for you, so the next steps are about your own figures.
2. Gather your records. Download the full history from every exchange and wallet you have used, including accounts you have closed. If you also sold shares or funds in the same years, get those broker exports too, because the annual exempt amount and losses are shared across both.
3. Work out each year's gains. Count every disposal, not just sales for pounds: swaps, spending and gifts count too (CRYPTO22100). Staking, lending and mining rewards are usually income, not gains (GOV.UK).
4. Compare with what you reported. If your returns already include the right figures, or nothing was taxable or reportable, you have your answer. If not, choose the route below that fits each year.
5. Reply by the date on the letter. Amend, disclose, or explain why nothing is owed. If you need more time, contact HMRC before the deadline using the details in the letter.
6. Pay what is due. Extra tax from an amendment is payable with interest. Through the disclosure service, you pay within 30 days of submitting.

Working out the figures

How crypto is taxed

For most individuals, crypto is a chargeable asset and gains go through capital gains tax (HMRC guidance). The matching rules mirror the ones for shares: tokens bought on the same day as a sale are matched first, then tokens bought in the next 30 days, and the rest sit in a pool at average cost, with a separate pool for each type of token (CRYPTO22200). An exchange's own statement is not a tax calculation, because it does not track your pooled cost across every platform.

Allowances and when you must report

The allowance applies to all your gains in the year, crypto and shares together (rates and allowances). If you are registered for Self Assessment, you must also report disposals when total proceeds go over the threshold, even if the gains are below the allowance (GOV.UK).

Where crypto goes on the SA108

From 2024/25, the SA108 capital gains pages have a Cryptoassets section, boxes 13.1 to 13.8 (SA108 forms and notes). On the 2025/26 form:

For 2023/24 and earlier there was no crypto section, and crypto went in Other property, assets and gains. Listed shares have their own section, boxes 23 to 30 on recent forms.

Doing it with FiscalFox

FiscalFox does not read exchange or wallet files directly. For crypto, it reads the Koinly Capital Gains Report: connect your exchanges and wallets to Koinly, set the country to United Kingdom and the currency to GBP, and download the Capital Gains Report as CSV for each tax year. Koinly has already matched every sale under the UK rules, and FiscalFox reports each line as Koinly worked it out. Upload it next to your broker exports, and FiscalFox adds your share gains, calculated under the same-day, 30-day and Section 104 rules, to give one set of figures by SA108 section for the year.

If the same coin appears in Koinly and in a broker file, FiscalFox asks whether Koinly already includes that broker account, so the sale is not counted twice. The import does not cover staking or other crypto income (Koinly's Income Report) or crypto futures and margin trades, so those need dealing with separately. The crypto and shares guide walks through it, the Koinly review covers the settings to check first, and the crypto tax software comparison covers the alternatives.

Calculating is free. The report pack for a tax year costs £39.99, paid once, and each extra tax year is bought separately. If a file will not import, the upload dialog offers a done-for-you report for £100, prepared within 2 working days or refunded in full.

Fixing earlier years

Amending a return

You can correct a Self Assessment return within 12 months of the filing deadline, online or on paper. For 2024/25, that usually means by 31 January 2027 (GOV.UK). The 2023/24 window closed on 31 January 2026, so older years go through a disclosure instead.

The cryptoasset disclosure service

HMRC's online service for unpaid tax on crypto income and gains needs a GOV.UK sign-in. You work out the tax, interest and any penalty for each year yourself, submit the disclosure, and pay within 30 days of submitting. HMRC then checks it and writes to say whether it accepts your offer. How many years you cover depends on why the tax was not paid: 4 years if you took reasonable care, and up to 6 years if you did not take enough care (GOV.UK). The same page explains the longer period that applies in other cases. Unpaid tax that is not about crypto, such as unreported share gains, uses HMRC's general disclosure route instead (GOV.UK).

Penalties and interest

HMRC's factsheet CC/FS7a sets out penalties for errors in returns (GOV.UK). Most crypto mistakes come from not knowing that a swap is a disposal, or from missing records, and for those the ranges are:

Penalties are reduced for telling HMRC about the error, helping it work out the figures and giving access to records, and the reduction is larger the sooner you do this. Interest runs from the date the tax was due until it is paid, at the Bank of England base rate plus 4% since 6 April 2025 (HMRC interest rates). The disclosure service rejects a disclosure that leaves out the interest.

If you have never been in Self Assessment and need to report gains, register first. For 2025/26 the registration deadline was 5 October 2026, so if you have missed it, register as soon as you can (GOV.UK).

When to get an accountant or tax adviser

FiscalFox calculates. It does not give tax advice, decide which route is right for you, contact HMRC, file your return or make a disclosure on your behalf. Many people with a few years of straightforward trades can do this themselves, but it is worth paying for professional advice if:

• HMRC has opened a formal enquiry or compliance check, rather than sending a general letter
• you are not sure whether an error counts as careless, or several years and larger sums are involved
• you have DeFi lending, liquidity pools, staking, mining or airdrops, or you trade so often it may be a business
• you were not UK resident for part of the period, or the crypto belonged to a company or trust
• you also need to correct other income or gains, or cannot pay what is due

The CIOT recommends checking that an adviser is properly qualified (CIOT guidance), and ICAEW has a directory of chartered accountants. If your income is low, the charity TaxAid may be able to help for free. Your FiscalFox report pack gives an adviser the disposal-by-disposal workings to start from.