Introduction: Crypto Tax for US Citizens Means Two Rulebooks, One Wallet
Crypto tax for US citizens living in Britain is not simply British tax plus a form. Both countries tax the same disposal. Crucially, they calculate it differently.
HMRC pools every unit of a token into one average cost. America now demands wallet-by-wallet tracking instead. Consequently, a single sale can produce two entirely different gains, and both are correct.
At TaxYork we prepare both returns for wealthy investors, traders and founders holding digital assets in London. This guide sets out where the two systems agree, where they diverge, and how to reconcile them. Furthermore, it covers the new reporting that started this year on both sides of the Atlantic.
What Crypto Tax for US Citizens Looks Like in Each System
Both countries reached the same starting point by different routes. Neither treats a token as money.
Crypto Tax for US Citizens Starts With Property, Not Currency
The IRS treats digital assets as property under Notice 2014-21, as its digital assets guidance confirms. Gains are capital gains, reported on Form 8949 and Schedule D.
HMRC takes a parallel view. Its cryptoassets manual treats tokens as chargeable assets for capital gains tax. Therefore, the character of the gain rarely differs. The measurement does.
What Counts as a Disposal in Both Countries
Selling for cash is obvious. Less obvious, and far more common, is the crypto-to-crypto swap. Both HMRC and the IRS treat exchanging one token for another as a disposal at market value.
Spending crypto also disposes of it. So does gifting to anyone other than a spouse. Accordingly, a portfolio rebalance across twelve tokens can generate twelve taxable events in each country on the same day.
Where Income Replaces Capital Gains
Mining, staking and payment for services usually produce income rather than gains. The rate and the timing then differ from the capital treatment entirely.
Frequent trading rarely converts an individual into a trader for British purposes. HMRC applies the badges of trade, and it accepts trading treatment only in exceptional cases. America has its own separate test, so the two answers can genuinely diverge.
The Matching Rules That Make the Two Gains Different
This section is where the money sits, and where almost every generalist guide stops.
Britain Pools Everything Into a Section 104 Pool
HMRC requires a single section 104 pool for each token, holding the aggregate cost of every unit you own. The pooling rules apply because tokens are fungible and dealt in without identifying particular units.
Your wallets are irrelevant to that pool. Ten wallets holding one token still produce one pool and one average cost. Notably, non-fungible tokens fall outside pooling entirely, because each is separately identifiable.
The Same-Day and Thirty-Day Rules Come First
Disposals are matched in a strict order. Acquisitions on the same day match first, under section 105. Next come acquisitions in the following 30 days, under section 106A, matched earliest disposal first.
Only the remainder touches the section 104 pool. Consequently, the pool average is not always the cost you use, and the order matters more than the arithmetic.
America Now Requires Wallet-by-Wallet Basis
Revenue Procedure 2024-28 ended universal cost basis tracking. From 1 January 2025, each wallet and each account is a separate ledger with its own basis.
The safe harbour allowed a one-off allocation of unused basis across wallets as at that date. That window has now closed for most filers. Therefore, whatever allocation you made then is the allocation you keep.
Why the Same Sale Produces Two Different Numbers
Put the two rules together. Britain averages your cheapest and dearest coins into one figure. America uses the actual cost sitting in the wallet you sold from.
Sell from an expensive wallet and your American gain is small while your British gain is large. Sell from a cheap wallet and the position reverses. Accordingly, which wallet you sell from is a real decision with a real cost.
Loss Harvesting: Allowed in America, Blocked in Britain
There Is Still No Wash Sale Rule for Ordinary Crypto
Section 1091 disallows a loss where you repurchase substantially identical stock or securities within 30 days. The statute says stock or securities, and ordinary cryptoassets are neither.
That gap survives into 2026. Only tokenised securities fall inside the rule, as the Form 1099-DA instructions reflect. Bills before Congress would extend section 1091 to digital assets, yet none has passed.
The Thirty-Day Rule Undoes the Same Trade in Britain
Britain closed this door years ago. Sell at a loss and rebuy within 30 days, and section 106A matches the repurchase to your disposal. The loss simply does not arise.
The asymmetry is therefore complete. One transaction creates a deductible American loss and no British loss whatsoever.
What Actually Works Across Both Systems
Waiting 31 days before repurchasing preserves the loss in both countries. Alternatively, buying a genuinely different token avoids the British matching rules while keeping market exposure.
Neither route is free of risk. Meanwhile, we model the British cost of a harvested American loss before recommending anything. An unusable American loss is worth nothing to a client whose UK tax already exceeds their US tax.
Making the Foreign Tax Credit Work on a Crypto Gain
Sourcing the Gain Under Section 865
A foreign tax credit needs foreign-source income. Section 865 sources gains on personal property to the seller's residence. A US citizen resident in Britain can therefore treat the gain as foreign-source.
That treatment requires the foreign country to tax the gain at 10% or more, and the US-UK treaty does not override the point. Britain charges 24% at the higher rate, so the test is comfortably met. Consequently, Form 1116 relief is generally available on a crypto gain, which is not true of every British asset.
The Tax Year Mismatch
Britain runs to 5 April and America to 31 December. A disposal in February therefore falls into different tax years in each country.
Credits are claimed on the cash basis by default, so the British tax may be paid in a later American year. Accordingly, we map the payment dates before filing rather than afterwards.
The 3.8% That Britain Never Relieves
Net investment income tax applies to crypto gains at 3.8%. As the IRS explains, it is a separate charge, and no foreign tax credit reduces it.
British tax therefore relieves your regular American tax but never this surcharge. On a large gain the 3.8% is simply payable, and clients should budget for it as a real cost.
Reporting: CARF, Form 1099-DA and the FBAR Question
The Cryptoasset Reporting Framework Started This January
Britain adopted the Cryptoasset Reporting Framework from 1 January 2026. Exchanges and brokers now collect user identity and transaction data, then report it to HMRC between January and May 2027 for the 2026 calendar year.
Penalties reach £300 per user for failures. Consequently, expect exchanges to demand tax residence details, and expect restrictions where you do not supply them.
Form 1099-DA and What Brokers Now Send
American brokers report digital asset sales on Form 1099-DA. The final broker regulations phase in gross proceeds first and basis afterwards.
Reported basis will often disagree with yours. A broker knows only what happened on its own platform, so transferred-in coins frequently arrive with no basis at all. Therefore, keep your own records regardless of what the form says.
Crypto and the FBAR: Still Outside, For Now
An account holding only cryptoassets is still not an FBAR reportable account. FinCEN proposed to change that years ago and has not finalised it, so the FBAR rules remain as they were.
The exception matters. An exchange account holding fiat currency alongside your tokens is reportable, and most large accounts do hold some fiat. Many published guides state the opposite in both directions.
Form 8938 Is a Different Question
Foreign account reporting under Form 8938 is broader than the FBAR. Digital assets held through a foreign exchange can be specified foreign financial assets, and the thresholds abroad start at $200,000.
Treat the two forms separately. Answering the FBAR question does not answer the FATCA one.
Staking, Airdrops, Forks and DeFi
Staking Rewards Are Income, at Different Moments
America taxes staking rewards as ordinary income when you gain dominion and control over them. Britain generally taxes them as miscellaneous income, valued at receipt.
The valuations therefore rarely match, because the moment of receipt is defined differently. Additionally, the sterling and dollar values move between those moments, which creates a second discrepancy on the same reward.
Airdrops and Forks
An airdrop received without doing anything in return may escape British income tax, though it still enters your pool at nil cost. America is generally less forgiving and taxes receipt.
Keep the date, the quantity and the market value of every airdrop. Reconstructing them two years later is close to impossible.
DeFi Lending and Liquidity Provision
HMRC treats many DeFi transactions as disposals where beneficial ownership passes. Consequently, depositing tokens into a liquidity pool can trigger British capital gains tax without any cash changing hands.
America has issued far less guidance here. We document the position taken and the reasoning, because a defensible contemporaneous analysis is worth a great deal if either authority asks later.
Correcting Earlier Years Before the CARF Data Lands
The Data Arriving in 2027 Reaches Backwards
CARF reports cover calendar year 2026 and land with HMRC by May 2027. Many exchanges, however, hold years of history on the same accounts.
A nudge letter naming an exchange is therefore a realistic prospect for anyone who has not reported past disposals. Acting first is materially cheaper than answering afterwards.
The Two Countries Allow Very Different Time Limits
HMRC can assess offshore matters for up to twelve years under section 36A of the Taxes Management Act 1970. Deliberate behaviour extends that to twenty.
One subsection matters here. Section 36A(7) shuts the twelve-year window where HMRC already held the information through automatic exchange. Consequently, CARF data can eventually narrow HMRC's reach rather than widen it, though only for the years it actually covers.
Sequencing a Correction Across Both Systems
America and Britain run separate correction routes, and the order matters. A British disclosure that changes your UK tax also changes the foreign tax credit on returns already filed in America.
Fix the records first, then the British position, then the American amendments. Additionally, gather exchange exports before you approach anyone, because a closed account rarely yields its history afterwards.
A Worked Case Study: A Mayfair Portfolio Manager and One Ethereum Sale
An American portfolio manager living in Mayfair came to us in July 2026 after selling part of his ether position.
What He Held
He had accumulated 400 ETH across three wallets. Wallet A held 150 units bought at £1,100, Wallet B held 150 units at £2,400, and Wallet C held 100 units at £3,600. His total cost was therefore £885,000.
In June 2026 he sold the 100 units held in Wallet C at £4,900 each, realising £490,000.
Two Correct Gains on One Sale
Britain pooled all 400 units, giving an average cost of £2,212.50. The British gain was therefore £490,000 less £221,250, or £268,750. After the £3,000 annual exempt amount, capital gains tax at 24% came to £63,780.
America looked only at Wallet C. Basis there was £360,000, so the American gain was £130,000. The same disposal produced gains differing by £138,750.
What He Actually Paid
Regular American tax at 20% on £130,000 came to £26,000, fully covered by the British credit. Net investment income tax at 3.8% added £4,940, and no credit touched it.
He therefore paid £63,780 in Britain and £4,940 in America. Additionally, £37,780 of excess foreign tax credit went into the passive basket, where it will carry forward for ten years.
The Loss He Nearly Wasted
He had also sold 50 units at a loss in November and repurchased five days later. America allowed that loss in full. Britain matched the repurchase under the 30-day rule and denied it entirely.
Had he waited 31 days, the loss would have counted in both countries. Consequently, a five-day decision cost him roughly £19,000 of British relief.
How TaxYork Can Help
We prepare both returns together and reconcile the two cost bases properly. Our team rebuilds section 104 pools from transaction history, applies the American wallet-by-wallet rules, and documents every position taken.
Furthermore, clients facing CARF letters or unreported prior years use our catch-up and disclosure service. Those with exchange accounts and foreign holdings rely on our FBAR and FATCA team, while stranded credits sit with our treaty and foreign tax credit specialists. Clients planning a large disposal should speak to our cross-border planning team first. Our note on Form 1099-DA covers the American reporting in more detail.
Conclusion
Crypto tax for US citizens in Britain is a reconciliation exercise, not a translation. The two systems agree that tokens are property and then part company on cost.
Track every wallet separately for America and pool everything for Britain. Wait 31 days before repurchasing. Budget for the 3.8% that no credit relieves. Ultimately, the records you keep this year decide how defensible your position looks when CARF data reaches HMRC in 2027.
Contact Us
Holding digital assets across both countries? Email hello@taxyork.com or call 020 3488 8606, or book a consultation and we will reconcile your pools and wallets before you file.
Disclaimer
This article provides general information only and does not constitute tax advice. Tax rules for digital assets change frequently, and their application depends on individual circumstances. You should obtain professional advice tailored to your position before acting. TaxYork accepts no liability for any action taken in reliance on this article. Further guidance is available from ICAEW, the Chartered Institute of Taxation, the AICPA and MoneyHelper, together with GOV.UK guidance on paying tax when you sell cryptoassets and the IRS page on Form 8949.