HMRC Crypto Nudge Letter: What to Do Next

HMRC has sent over 100,000 capital gains tax warning letters to crypto investors since 2020. The pace is accelerating: 8,329 in 2021/22, 27,712 in 2023/24, and 64,982 in 2024/25 alone. That's a 680% increase in three years.

If you've bought, sold, swapped, staked, or provided liquidity with crypto, HMRC may already hold exchange-side information. From January 2026, in-scope providers also began CARF due diligence, record keeping, and data collection; their first reports are due by 31 May 2027.

This guide explains what's happening, what it means for you, and what you need to do before the next self-assessment deadline.

What are the warning letters?

HMRC calls them "one to many" nudge letters, and some arrive as emails rather than post. They're sent to taxpayers whose records suggest they've sold, exchanged, or received crypto without fully declaring the gains or income on their tax return.

The letters aren't accusatory, and HMRC frames them as "encouraging voluntary compliance." But make no mistake: if you receive one, HMRC already has data suggesting a discrepancy between what you declared and what your exchange reported.

Crypto investors have received 40 times more CGT warning letters than stock traders since 2020. HMRC is clearly treating crypto as a priority enforcement area.

Why now? CARF changes everything

The real shift happened on 1 January 2026, when the Crypto-Asset Reporting Framework (CARF) came into force in the UK. This is an OECD-designed framework that requires crypto platforms to report user transaction data directly to tax authorities.

Around 50 UK crypto service providers (exchanges, custodial wallet providers, and some DeFi platforms with controlling entities) are now collecting and reporting:

• Your name, address, date of birth, and tax residency
• Your National Insurance number or tax reference
• Full transaction records: purchase price, sale price, profits
• Every disposal, sale, swap, and transfer
• Annual transaction summaries

The first reports are due to HMRC by 31 May 2027, covering the 2026 calendar year. But HMRC already has historical data from exchanges collected under existing Finance Act powers. CARF just makes the reporting automatic, comprehensive, and standardised.

What HMRC can see now vs before

The Treasury estimates CARF will raise £315 million in unpaid tax by 2030. That money has to come from somewhere, and it's coming from the returns HMRC can now cross-check against exchange-reported data.

What counts as a taxable event

Many investors assume they only owe tax when they "cash out" to GBP. That's wrong. HMRC treats all of the following as disposals that trigger Capital Gains Tax:

• Selling crypto for GBP or any fiat currency
• Swapping one crypto for another (including ETH → USDC)
• Paying for goods or services with crypto

Liquidity and liquid-staking positions are fact-specific. A disposal can arise where beneficial ownership transfers or the rights received are materially different; a different token is evidence to examine, not a conclusive rule by itself.

Note on bridging: Cross-chain bridges (e.g. ETH from Ethereum to Arbitrum) are a grey area. HMRC has not explicitly ruled on bridges. The conservative view is that bridging transfers your cost basis across chains without triggering a disposal, since you hold the same asset on a different network. Some advisers take the opposite position. If you have significant bridging activity, get professional advice.

Additionally, staking rewards, airdrops, and mining receipts can create taxable miscellaneous or trading income, depending on how they were earned and the wider facts.

The penalties for getting it wrong

HMRC's penalty regime is tiered based on the severity of the error:

On top of penalties, HMRC charges daily interest on outstanding balances, plus late payment surcharges of 5% at 30 days, 6 months, and 12 months.

The investigation lookback periods are also tiered: 4 years for innocent errors, 6 years for careless errors, and up to 20 years for deliberate non-disclosure. With CARF data flowing from 2027, HMRC will have the evidence to pursue cases going back years.

What to do before the deadline in your letter

1. Check if you have undeclared disposals. Crypto-to-crypto swaps are normally disposals. Liquidity and staking activity is fact-specific and can contain transfers, disposals, income, and fees. If you only reviewed GBP cash-outs, the history may be incomplete.
2. Gather your transaction history. Export data from every exchange and wallet you've used. For DeFi activity, you'll need on-chain data from block explorers, because exchange CSVs won't capture it.
3. Calculate your gains correctly. HMRC requires Section 104 pooling with same-day and 30-day bed-and-breakfast matching rules. A simple "bought at X, sold at Y" calculation is not sufficient. See our 2025/26 self-assessment filing guide → (or our complete 2024/25 guide for the now-closed year).
4. Separate income from capital gains. Staking rewards, airdrops, and LP fees can create income depending on the arrangement. Token disposals are considered separately for CGT. These can go on different parts of your self-assessment, and once your DeFi income is large enough, it can pull you into payments on account the following year. Read our staking tax guide →
5. Amend past returns if needed. You can amend a return within 12 months of the filing deadline. Beyond that, HMRC's Cryptoasset Disclosure Service may be relevant. The correct route and penalty treatment depend on the facts.
6. Don't ignore the letter. Use the response date printed on your letter. Ignoring it does not close the matter and may lead to further compliance action.

How to reply to the letter

Once you've recalculated your figures, the nudge letter resolves to one of three honest outcomes:

1. Your returns were right. If your recalculated gains match what you declared, reply by the deadline in the letter confirming you've reviewed your position and no amendment is needed. Keep the full calculation, because HMRC can ask how you reached it, and a Section 104 computation that shows its working is exactly what they want to see.
2. You under-declared, and the year is still amendable. You can amend a return within 12 months of its filing deadline, so a 2024/25 return filed online can be amended until 31 January 2027. Amend, pay the difference plus interest, and the matter usually ends there.
3. Older years are affected. Use HMRC's Cryptoasset Disclosure Service, and our voluntary disclosure guide explains the current GOV.UK process and evidence needed. Contact from HMRC can be relevant to whether a disclosure is prompted, but the position is fact-specific and should be checked before submitting. Do not wait for a formal enquiry.

The bigger picture

The UK is part of an initial group of 48 countries implementing CARF simultaneously. From 2027, these countries will automatically share crypto transaction data with each other. Using an overseas exchange doesn't help. If it operates in a CARF jurisdiction, the data is shared with HMRC anyway.

HMRC already has exchange-side information and CARF will create a more structured reporting source. In-scope providers first report 2026 activity by 31 May 2027; the exact operational matching process is still developing.

The good news: if you get your records in order now, you're ahead of the curve. Most crypto investors haven't. That's why HMRC expects to collect £315 million in unpaid tax by 2030.

Start with the basics: check whether you need to report crypto to HMRC at all, then make sure your Section 104 pool and exchange records agree.