UK Crypto Swaps and CGT: Why No Cash Changes Hands and Tax Still Applies

The most common UK crypto tax misunderstanding is also the most expensive one: "I never cashed out, so I owe nothing." Under HMRC rules, that is wrong. A crypto-to-crypto swap is a disposal for Capital Gains Tax, even when no pounds ever appear.

This version covers the UK only, for the 2026/27 tax year (6 April 2026 to 5 April 2027). US rules are different and are not mixed in here.

The core rule

HMRC treats most individuals' crypto as a personal investment, similar to shares — not as money. CGT applies on disposal, and HMRC's disposal list includes exchanging one type of crypto for another. Selling for pounds, swapping tokens, paying for goods with crypto, and giving crypto away (with different treatment for gifts to a spouse or civil partner) all count.

Two non-events are worth stating plainly, because they cause equal confusion in the other direction: buying with pounds and holding creates no tax, and moving coins between wallets owned by the same person is not a disposal.

How the gain is actually calculated

Gain = pound value received minus pound cost of the part given up, with allowable purchase and swap fees deductible. The subtle part is the cost figure, because HMRC matching rules decide which cost applies, in this order:

1. Same-day rule — coins of the same type bought on the same day as the disposal.
2. 30-day rule — coins of the same type bought within 30 days after the disposal.
3. Section 104 pool — everything else, averaged across all holdings of that coin type.

The pool rule is where manual calculations go wrong. Worked example, with made-up numbers:

Buy 1 ETH for £2,000, then another 1 ETH for £3,000. The pool holds 2 ETH at a total cost of £5,000, so the average cost is £2,500 per ETH. Swap 1 ETH when it is worth £4,000. The cost used is £2,500 — not £2,000, not £3,000 — giving a gain of £1,500.

Two simpler examples that show the allowance at work

Inside the allowance: Buy 1 ETH for £2,000, swap it for SOL when it is worth £3,000. Gain = £1,000. If that is the only disposal in the year, it sits below the £3,000 annual exempt amount for 2026/27, so no CGT is payable — but the record should still be kept.

Above the allowance: Total gains for the year are £5,000. Subtract the £3,000 allowance, leaving £2,000 taxable. At the 18% basic rate, that is £360. The rate is 18% or 24% depending on income and how much of the gain falls into each band; GOV.UK carries the current rates.

Reporting, losses, and records

Gains above the £3,000 allowance are normally reported on a Self Assessment return. Reporting can also be required when proceeds pass £50,000 even if the gain itself is small, so the £3,000 figure alone is not a complete test. Registration is generally due by 5 October after the end of the relevant tax year, and online filing by the following 31 January — HMRC guidance is the final word on dates.

Losses can reduce gains, but carrying a loss forward generally requires reporting it, normally within four years of the end of the tax year it arose in. Losses are not assumed to carry forward automatically.

The record set for every transaction: date, coin type and amount, pound value that day and its price source, fees, and wallet or exchange used. Exchange CSV exports are a starting point; tax software exists precisely because the same-day, 30-day, and pool rules are tedious to apply by hand across many swaps.

The takeaway for builders and traders

Every swap is a taxable event in the UK, stablecoin swaps included. The practical fix is boring and effective: log each swap as it happens, with its pound value, rather than reconstructing a year of trades at filing time.

This is general information, not tax advice. Rules change and individual situations differ — check GOV.UK guidance or a qualified UK tax adviser before acting.

Sources: HMRC Cryptoassets for individuals (GOV.UK); HMRC Cryptoassets Manual; CGT allowances and rates (GOV.UK).

Full guide: Is a Crypto-to-Crypto Swap Taxable in the UK? CGT Rules + Worked Examples (2026/27)