HMRC Crypto Tax Warning Letters, Autumn 2026: Got One? Here's Exactly What to Do

If HMRC has written to you about crypto this autumn, it's almost certainly a "one to many" warning letter, not an investigation. It means HMRC thinks you may have undeclared gains or income. You should check your figures, then either amend your return, use the cryptoasset disclosure service, or keep a note showing you owe nothing. Doing that before HMRC opens a formal check usually means lower penalties.

The numbers explain why so many people are suddenly searching for this. A Freedom of Information request reported by the BBC showed HMRC sent 81,172 crypto letters, emails and texts in the 2025/26 tax year, up from 64,982 the year before and 27,714 in 2023/24. And it isn't slowing down. ICAEW reported in July that HMRC's Wealthy and Mid-sized Business Compliance team will contact people it believes underpaid tax on crypto between July 2026 and March 2027.

We covered the basics in our earlier nudge letter guide. This is the autumn 2026 update: what's new, the dates that matter, and a worked example in pounds.

What's different about the letters going out in autumn 2026?

Volume and data. The current campaign runs from July 2026 to March 2027, letters may also arrive by email, text or possibly the HMRC app, and agents get copies. HMRC also now receives data from UK crypto platforms under the Cryptoasset Reporting Framework, which started on 1 January 2026.

That last point changes the mood. Under CARF, UK platforms have been collecting your name, address, date of birth, tax residence and National Insurance number or UTR since January. Their first reports, covering calendar year 2026, are due between 1 January and 31 May 2027. UHY Hacker Young has said HMRC will receive data from 52 jurisdictions in 2027 and 15 more in 2028. Our CARF explainer covers how that sharing works.

So the letters landing now are, if anything, the gentle phase. The data-driven phase comes next year.

Do I have to reply to an HMRC crypto letter?

Not always. ICAEW's summary of the campaign says no action is needed if you believe you have no income or gains to report. If you do have something to declare, you should amend your Self Assessment return or, where it's too late to amend, use HMRC's cryptoasset disclosure service.

In practice, "no action" should still mean doing the sums. Being out of pocket on crypto doesn't automatically mean there's nothing to report, because every swap of one token for another is a disposal. If you've done that work and you're within the rules, save your calculations. If HMRC follows up, you'll have them ready.

Photo via Unsplash

What are the deadlines I need to know?

The key one for most people is 31 January 2027. That's the last day to amend a 2024/25 return and the filing deadline for 2025/26 returns. For years you can no longer amend, the disclosure service applies, and once you submit a disclosure you have 30 days to pay.

What	Deadline
Amend a 2024/25 Self Assessment return	31 January 2027
File and pay for 2025/26 (online)	31 January 2027
Payment reference after a disclosure	Within 15 working days (chase HMRC if not)
Pay tax, interest and penalty after disclosing	Within 30 days of submitting
HMRC's current letter campaign	July 2026 to March 2027

If your letter itself gives a date to respond by, treat that as your real deadline, whatever the general rules say.

How does the cryptoasset disclosure service work?

It's an online form on GOV.UK for declaring unpaid Capital Gains Tax or Income Tax on crypto from earlier years. You work out the tax, interest and penalty yourself, submit one offer for the full amount, then pay. Current and last year's figures go on your normal return instead.

GOV.UK sets out the steps. You decide how many years to cover, which depends on your behaviour: four years if you took reasonable care, six if you were careless, up to 20 if it was deliberate. You'll need the number of transactions, proceeds, costs, the exchanges you used and your calculations. HMRC then checks the disclosure and either accepts your offer or tells you why it can't. Our voluntary disclosure guide walks through the form in more detail.

What penalties could I face?

It depends on why the tax was missed and whether you came forward before HMRC prompted you. Careless errors carry 0% to 30% of the unpaid tax if unprompted, 15% to 30% if prompted. Deliberate errors run up to 70%, and deliberate and concealed up to 100%. Offshore matters can carry more.

Here's HMRC's own table from its Compliance Handbook:

Behaviour	Unprompted	Prompted
Careless	0% to 30%	15% to 30%
Deliberate	20% to 70%	35% to 70%
Deliberate and concealed	30% to 100%	50% to 100%

Whether a disclosure made after a general warning letter counts as prompted or unprompted depends on the facts, so don't assume either way. My view? The letter is a gift of time. Most people who get one have made a careless mistake, not committed fraud, and the cheapest outcome is nearly always sorting it out now.

A worked example. Say you sold bitcoin for £20,000 in 2023/24 that had cost you £8,000. Your gain is £12,000. The annual exempt amount that year was £6,000, leaving £6,000 taxable. At the 20% higher rate that applied to crypto then, the tax is £1,200. Add late payment interest, and a careless-error penalty of between nothing and £360 if unprompted. Our gains calculation guide explains the pooling rules behind the cost figure.

Frequently asked questions

How many crypto tax warning letters has HMRC sent? A Freedom of Information request reported by the BBC showed 81,172 letters, emails and texts in the 2025/26 tax year. That's up from 64,982 in 2024/25 and 27,714 in 2023/24, and a further campaign runs from July 2026 to March 2027.

Is an HMRC crypto warning letter an investigation? No. It's a prompt to check your tax position, not an assessment or a formal enquiry. HMRC may open a check later if you don't respond and its data still suggests tax is missing, so it's worth acting on.

Can I ignore the letter if I owe nothing? ICAEW says no action is needed if you believe you have no income or gains to report. Do the calculation properly first, including crypto-to-crypto swaps, and keep your workings in case HMRC asks.

How long do I have to pay after a disclosure? GOV.UK says you should pay within 30 days of submitting your disclosure. HMRC sends a payment reference by letter, and you should contact the helpline if it hasn't arrived within 15 working days.

How far back can HMRC go on crypto tax? Usually four years if you took reasonable care, six if you were careless and up to 20 if the underpayment was deliberate. The disclosure service asks you to choose the right period based on that.

Your next step

Pull full transaction histories from every exchange and wallet, work out each year's gains, then pick the right route: amend, disclose or file the workings away. If it's messy, a crypto-savvy accountant is money well spent. This isn't tax advice. For background, see can HMRC see my crypto? and our Self Assessment guide.