If you are a US citizen living in the UK and you hold cryptoassets, you are running two completely separate tax computations over the same wallet. HMRC treats crypto as a chargeable asset subject to Capital Gains Tax and requires you to pool identical tokens into a single averaged cost, adjusted by same-day and 30-day matching rules. The IRS treats crypto as property, tracks each acquisition as its own lot with its own basis, and lets you choose between FIFO and specific identification. The two systems produce different gains on identical trades, in different currencies, over tax years that do not align. Neither country cares that the other exists, and the foreign tax credit that is supposed to prevent double taxation frequently fails to bridge the gap. This is the most common cross-border reporting failure we see, and it is almost always a mechanical problem rather than an avoidance one.
What each country thinks crypto is
HMRC's position, set out in its Cryptoassets Manual, is that for most individuals cryptoassets are investments held as capital assets. Buying and holding is not taxable; disposing is. A disposal includes selling for fiat, swapping one token for another, spending crypto on goods or services, and gifting it to anyone other than a spouse or civil partner. Trading as a business is possible but rare — HMRC applies the badges of trade and sets a high bar, so the overwhelming majority of individuals are taxed under CGT rather than as traders.
The IRS reached the same starting point by a different route. Notice 2014-21 established that virtual currency is treated as property for federal tax purposes, so general property principles apply: gain or loss on every disposition, short-term or long-term depending on the holding period, reported on Form 8949 and Schedule D.
So far the two systems agree. The agreement ends the moment you have bought the same token more than once.
The pooling problem: HMRC's section 104 pool versus US lots
Under UK rules, all units of the same token are treated as a single asset — the section 104 pool — with one averaged cost. Buy 1 ETH at £1,500 and another at £2,500, and your pool is 2 ETH with a total cost of £4,000, so every fraction of an ETH you dispose of has a base cost of £2,000. You cannot choose which one you sold, because in UK law you did not sell a particular one.
Under US rules the two ETH remain two distinct lots with bases of their dollar equivalents at acquisition. When you sell one, you either take the first lot under FIFO or you specifically identify a lot, provided you meet the identification requirements at the time of the sale. The choice affects both the amount of the gain and whether it is short-term or long-term.
The consequence is that the same disposal generates a genuinely different gain in each country, and not merely because of exchange rates. Sell one ETH from that pool for £3,000 and the UK sees a £1,000 gain against the averaged £2,000 base cost. The US, using specific identification of the higher-cost lot, might see a much smaller gain, or a loss. There is no reconciliation between them — you simply have to compute both.
The 30-day rule and the absence of a US equivalent
UK matching rules override the pool in two situations. Acquisitions on the same day as a disposal are matched against that disposal first. Then acquisitions in the 30 days following the disposal are matched next, on a first-in-first-out basis. Only after those are exhausted does the disposal come out of the section 104 pool. These are the 'bed and breakfasting' rules, and they exist to stop people crystallising a gain or loss and immediately buying back.
The United States has a wash sale rule at section 1091, but by its terms it applies to stock and securities. Cryptoassets have generally been understood to fall outside it, which is why crypto tax-loss harvesting has been common in the US in a way it cannot be in the UK. Proposals to extend the rule to digital assets have circulated for several years, so this is a point to check for the year you are filing rather than to assume permanently.
For an American in the UK the asymmetry cuts both ways: a sale-and-repurchase inside 30 days may be effective for US loss purposes but disallowed in the UK, leaving you with a US loss and no UK one on the same trade.
Rates: what each side actually charges
In the UK, cryptoasset gains are charged to Capital Gains Tax at 18% to the extent they fall within your unused basic rate band and 24% above it, after deducting the annual exempt amount of £3,000. Gains stack on top of your income, so a higher-rate earner pays 24% on essentially all of it. You can model this on our UK capital gains tax calculator.
In the US, the rate depends entirely on the holding period. Held for one year or less, the gain is short-term and taxed at your ordinary income rates. Held for more than a year, it is long-term and taxed at 0%, 15% or 20% depending on your income. On top of that, the 3.8% Net Investment Income Tax applies to investment income above the threshold — and, importantly, the IRS position is that NIIT sits outside the treaty's relief-from-double-taxation article, so UK tax generally cannot be credited against it. Our guide to the NIIT for expats covers that trap, and our US crypto capital gains calculator handles the US side.
The practical result for most higher-rate UK residents is that the UK rate of 24% exceeds the US long-term rate, so the foreign tax credit usually covers the US liability on long-term gains — but not the NIIT, and not necessarily on short-term gains where the timing goes wrong.
The tax year mismatch that breaks the foreign tax credit
The UK tax year runs from 6 April to 5 April. The US tax year is the calendar year. A gain realised on 20 February 2026 falls into UK 2025-26 and US 2026. The UK tax on it is not due until 31 January 2027, and is not even reported until the return for 2025-26 is filed.
That creates a genuine problem for the foreign tax credit. If you claim the credit on the cash basis, you claim UK tax in the US year you paid it, which may be one or even two US years after the US year in which the income arose — and the credit has to be claimed in the same basket and against the same category of income. If you elect the accrual basis, the timing improves but the election is generally irrevocable and applies to all future years.
The practical fix is to plan disposals with both calendars in view. A disposal made in, say, May sits at the start of a UK tax year and comfortably inside a US calendar year, which keeps the two computations closer together than a disposal in late February or March does. Where the timing cannot be helped, carry-back and carry-forward of excess credits provides some relief, but only within the same basket. Our comparison of the foreign tax credit and the FEIE explains the mechanics, and the foreign tax credit calculator helps size the limitation.
Currency: two different sterling problems
The UK computes the gain in sterling. The US computes it in dollars. Both require you to translate at the rate on the date of each acquisition and each disposal — not an annual average, and not the rate on the day you happened to move the money.
This means exchange rate movement between acquisition and disposal is itself part of the US gain. A token bought and sold for exactly the same amount of sterling produces a US gain if the dollar weakened in between, and a US loss if it strengthened. The UK sees nothing at all, because in sterling terms nothing happened. There is no UK tax to credit against that gain, so it is taxed in the US with no relief.
For anyone who moved to the UK with an existing crypto position, this is compounded by the fact that your US basis was fixed in dollars long before you arrived, while your UK base cost is whatever you actually paid — which for UK purposes may need to be established in sterling at the historic date. Keep the acquisition records in both currencies from day one.
Staking, mining, airdrops and other income events
Both countries treat rewards as income at receipt, and both then treat the disposal of the reward token as a separate capital event — but the detail differs.
HMRC's view is that staking and mining rewards are generally miscellaneous income taxable at income tax rates on the sterling value at receipt, unless the activity amounts to a trade, in which case trading rules apply. Airdrops are taxable as income where they are received in return for, or in expectation of, providing a service, and are not taxable at receipt where they are genuinely gratuitous — though the tokens still enter the pool at nil cost, so the whole proceeds become a gain on disposal.
The IRS position on staking rewards, set out in Revenue Ruling 2023-14, is that a cash-method taxpayer includes the fair market value of rewards in gross income in the year they gain dominion and control over them. That value then becomes the basis of the tokens. The dominion-and-control test can produce a different timing answer from HMRC's receipt test, particularly with locked or vesting rewards.
The recurring practical failure is basis. People report the income correctly and then, on disposal months later, report the entire proceeds as gain because they never recorded the value that was already taxed as income. That is straightforward double taxation, self-inflicted, and it is very common.
DeFi, wrapping and the transactions people do not realise are disposals
- Swapping token A for token B is a disposal of A in both countries, taxed on the sterling or dollar value received, even though no fiat changed hands.
- Spending crypto on goods or services is a disposal at market value on the date of spending.
- Wrapping and unwrapping tokens may be a disposal depending on whether beneficial ownership changes — HMRC's guidance turns on the facts of the particular protocol.
- Adding to and withdrawing from a liquidity pool can be a disposal where beneficial ownership of the deposited tokens passes to the pool.
- Lending crypto for a return can produce an income event on the return and a disposal on the loan itself, again depending on whether beneficial ownership transfers.
- Gifting to anyone other than a spouse or civil partner is a disposal at market value in the UK; in the US, gifts above the annual exclusion require a Form 709 but do not themselves trigger gain.
Form 1099-DA and the end of the record-keeping excuse
US broker reporting for digital assets has now arrived. Under the final regulations, brokers report gross proceeds for transactions effected on or after 1 January 2025, and must report basis on certain transactions effected on or after 1 January 2026. The instructions for Form 1099-DA set out the covered-security rules: broadly, a digital asset is a covered security only if it was acquired after 2025 in an account for which the broker provided custodial services and held in that account until disposal.
The practical consequence is that for 2025 disposals most statements carry proceeds but no basis, so taxpayers must compute basis themselves — and the IRS now has the proceeds figure regardless. A return that omits a disposal the IRS already has a 1099-DA for is a return that will generate a notice.
For an American in the UK, note what 1099-DA does not do: it is a US reporting regime, it does not compute your UK pool, and a non-US exchange is generally outside it. You may receive nothing at all from a UK or offshore platform while still having a full US reporting obligation.
Do you have to report crypto on the FBAR or Form 8938?
This is where careful answers matter. FinCEN signalled several years ago its intention to amend the FBAR regulations to include virtual currency as a reportable account, but until that amendment is in force, an account holding only virtual currency is generally not by itself an FBAR-reportable account. An account that holds fiat alongside crypto, or a crypto platform that also provides a foreign bank or securities account, can be reportable on ordinary principles.
Form 8938 is broader. Foreign financial assets held for investment can include an interest in a foreign entity or certain foreign-held digital asset arrangements, and the thresholds for a taxpayer living abroad are substantially higher than for FBAR — more than $200,000 on the last day of the year or more than $300,000 at any point during it, for a single filer.
Because the FBAR position is expected to change, the sensible approach is to keep a full record of every foreign platform and account balance by year, so that if the rules are amended you can look back rather than reconstruct. Our FBAR guide and our comparison of FBAR and FATCA set out the current thresholds.
Reporting the UK side
In the UK you report crypto gains through Self Assessment, on the capital gains pages, where total gains exceed the annual exempt amount of £3,000 or where total proceeds exceed the reporting threshold even if the gain is small. The return for 2025-26 is due by 31 January 2027 if filed online, with the tax due the same day.
You need to keep the type of token, the date of each transaction, the number of units, the value in sterling, the running pool total, and bank statements or wallet records. HMRC expects these to be retained for at least a year after the filing deadline for the relevant year, and considerably longer if the position is complex.
HMRC has been issuing nudge letters to individuals it believes hold cryptoassets, using data obtained from exchanges. If one arrives, it is not an accusation, but it is a firm signal that HMRC already has transaction data and expects the return to reflect it.
If you have not been reporting either side
The routes differ. In the UK, HMRC operates a dedicated disclosure service for unpaid tax on cryptoassets, and a voluntary disclosure before any enquiry opens materially reduces penalties. In the US, if the unreported crypto sits alongside unfiled returns or unreported foreign accounts and the conduct was non-wilful, the Streamlined Foreign Offshore Procedures can bring three years of returns and six years of FBARs up to date with no penalty for a qualifying taxpayer living abroad.
The order matters, and so does the consistency of the two stories. A disclosure to HMRC that describes trading activity one way and a US submission that describes it another is a problem waiting to happen, and both authorities exchange information. Get both computations built before either disclosure is filed.
