A very common and expensive belief among UK crypto holders is that Capital Gains Tax applies only when tokens are converted into pounds. The logic runs: “I swapped ETH for SOL, but I never actually cashed out, so no tax is due.”
That belief is wrong, and it has cost a significant number of investors unexpected tax bills and penalties. This page explains why every crypto-to-crypto swap is a taxable disposal under UK law, how the gain is calculated, what the rates are, and when you must report even if nothing is owed.
The short answer: yes, swapping crypto is a taxable disposal
Under HMRC guidance, swapping one cryptoasset for another is a disposal for Capital Gains Tax. The disposal is valued at the sterling market value of the token you gave up at the moment of the swap. “I never cashed out to pounds” is not a defence. The tax event is the exchange of assets, not the conversion to fiat currency. This applies to every token-for-token trade, including swaps for stablecoins.
This is not a grey area or an interpretation that might change. HMRC's cryptoassets manual and its published guidance are explicit. The obligation has existed since HMRC first published its approach to cryptoassets.
Why “I never cashed out to pounds” is not a defence
Capital Gains Tax applies to disposals of assets, not to conversions into sterling. HMRC's published guidance lists the events that count as disposals of cryptoassets:
- Selling crypto for fiat currency (GBP, USD, EUR, and so on)
- Swapping one token for another token
- Spending crypto on goods or services
- Gifting crypto to someone other than a spouse or civil partner
Source: gov.uk: Check if you need to pay tax when you sell cryptoassets.
Notice that “converting to GBP” is only one item on that list. The sale-to-fiat event is not special. Swapping ETH for SOL, trading BTC for USDC, or moving from one altcoin to another: each of these is a disposal of the token you gave up, at the time you gave it up.
The intuition behind the “I never cashed out” defence is understandable: you do not have pounds in your bank account, so where is the tax supposed to come from? The answer is that CGT is charged on the gain crystallised at the point of the swap, and the liability is payable in sterling through Self Assessment. If the proceeds of your swaps leave you with a tax liability but no pounds, you need to liquidate enough crypto to cover it. That is the reality of investing in volatile assets.
How the gain is measured: sterling market value at the moment of the swap
When you swap Token A for Token B, you have disposed of Token A. The proceeds of that disposal are the sterling market value of Token A at the exact moment of the swap (or equivalently, the sterling value of Token B received, whichever gives a fair arm's-length value).
Your gain is: Disposal proceeds minus your allowable cost in Token A.
Your allowable cost in Token A comes from the section 104 pool for that token. Each cryptoasset type has one pool, holding the aggregate cost of all tokens of that type you have acquired. The allowable cost for a disposal is the proportionate average cost of the pool at the time of the disposal.
This matters because UK rules are not FIFO (first in, first out), LIFO (last in, first out), or specific-identification. US crypto tax software often defaults to one of those methods, which gives the wrong answer for UK tax. If you are using imported figures from a US-based tool, verify that it is applying UK s104 pooling.
Two further rules override the pool for recent acquisitions: same-day acquisitions are matched first, then acquisitions in the following 30 days. These matching rules are the biggest single source of error in DIY crypto returns for anyone who trades actively, and they are outside the scope of any stateless web calculator. If your trading involves regular buys and sells, you need a full reconciliation.
A worked illustration: swapping ETH for SOL
The numbers below are illustrative example figures, not current market prices.
| Event | Detail | Sterling value |
|---|---|---|
| Acquisition of 2 ETH | Bought at £1,200 each, pool cost = £2,400 | £2,400 (cost) |
| Swap: 2 ETH for 40 SOL | ETH spot price at swap = £2,000 each; disposal proceeds = £4,000 | £4,000 (proceeds) |
| Gain on the swap | £4,000 proceeds minus £2,400 allowable cost | £1,600 gain |
That £1,600 gain is a taxable event. No pounds changed hands: you simply hold 40 SOL instead of 2 ETH. But HMRC treats it as a disposal of 2 ETH at their sterling market value on the date of the swap. The gain of £1,600 is set against the annual exempt amount (currently £3,000 for 2026/27). If this is your only disposal of the year, no tax is due and the remaining £1,400 of your exempt amount is available for future disposals in the same tax year.
Now consider what happens across a busier year.
Why this compounds: every swap in a year is a separate disposal, and the AEA goes fast
The annual exempt amount (AEA) for 2026/27 is £3,000. That is the total amount of gains in the year that are not subject to CGT. It does not refresh per disposal: it is one pool for the whole year.
Consider a holder who makes the following swaps over the tax year, each producing a modest gain:
| Disposal | Gain | Running total of gains | AEA remaining |
|---|---|---|---|
| Swap 1: BTC to ETH (Jan) | £900 | £900 | £2,100 |
| Swap 2: ETH to SOL (Mar) | £1,200 | £2,100 | £900 |
| Swap 3: SOL to AVAX (May) | £700 | £2,800 | £200 |
| Swap 4: AVAX to BTC (Aug) | £600 | £3,400 | Exhausted |
| Swap 5: BTC to ETH (Nov) | £800 | £4,200 | £0 |
By Swap 4, the AEA is exhausted. Swaps 4 and 5 produce £1,400 of gains that are fully exposed to CGT. None of these disposals touched pounds. This is how an investor who believes they have “not sold anything” can accumulate a CGT liability across a year of token-to-token trading.
The picture becomes more complicated where some swaps produce losses. Capital losses can be set against gains in the same year, and any excess can, once claimed, be carried forward indefinitely (the claim must normally be made within four years of the end of the relevant tax year). Getting the full picture requires a complete swap-by-swap reconstruction, not a rough estimate.
What you actually pay: CGT at 18% within the remaining basic band, 24% above
Cryptoassets are non-residential assets. The CGT rates for 2026/27 are:
- 18% on the portion of gains that falls within your remaining basic-rate income tax band
- 24% on any gains above that boundary
- 24% on the whole chargeable gain if you are a higher or additional-rate taxpayer
The basic-rate band ceiling is £37,700 of taxable income for 2026/27. “Remaining basic-rate band” means the gap between your taxable income and £37,700. If your employment or self-employment income already fills the basic-rate band, your crypto gains are taxed at 24% from the first pound of gain above the AEA.
A common presentation error is to state that basic-rate taxpayers pay a flat 18% on all crypto gains. That is wrong. The 18% rate applies only to the portion of the gain that fits inside the remaining band. Any gain above that ceiling is charged at 24%, even for basic-rate taxpayers. For someone with moderate income and a large gain, most of the gain will be taxed at 24%.
Worked example of the rate split:
| Item | Amount |
|---|---|
| Taxable employment income | £28,000 |
| Basic-rate band ceiling | £37,700 |
| Remaining basic-rate band | £9,700 |
| Total crypto gains for the year | £14,000 |
| Less AEA | £3,000 |
| Chargeable gain | £11,000 |
| CGT at 18% on first £9,700 (within band) | £1,746 |
| CGT at 24% on remaining £1,300 (above band) | £312 |
| Total CGT liability | £2,058 |
These are illustrative example figures. Your own income, gains, losses, and allowances will differ. A scenario estimate is available from the crypto CGT estimator (note: that tool uses pool-simplified assumptions and does not model the same-day or 30-day matching rules; it ends at “your situation has X complexity, speak to us”, not a filing-ready figure).
Scottish taxpayers should note that the basic-rate band boundary for Scottish income tax differs from the rest of the UK. However, CGT itself is a reserved tax applied UK-wide at the rates above; the Scottish income tax bands affect only the calculation of “remaining basic-rate band” in the rate-split calculation. If you are a Scottish taxpayer with income near the band boundaries, seek advice specific to your position.
Reporting even when no tax is due
A further misconception is that if the AEA covers all gains and no tax is owed, there is nothing to report.
Under HMRC rules, where your total disposal proceeds in a tax year exceed the reporting threshold, you must include those disposals in a Self Assessment tax return even if the AEA absorbs the whole gain and no tax is payable. The obligation is triggered by the level of proceeds, not by whether a tax bill results.
This means an investor who makes a large number of token swaps with a high aggregate value, but whose net gain is covered by the AEA and carried-forward losses, may still have a Self Assessment filing obligation. Failure to file when required to do so can result in late-filing penalties, even when the tax due is nil.
The Self Assessment registration deadline is 5 October following the end of the tax year in which the first reportable event arose. For disposals in the 2025/26 tax year (ending 5 April 2026), the registration deadline was 5 October 2026. If you missed it, disclosure is still preferable to continued non-filing.
If you are not sure whether your disposal proceeds exceed the reporting threshold, a full reconciliation of your swap history is the only reliable way to find out. A rough estimate is not enough: the threshold is a hard statutory test, not a soft guide.
Getting your swap history reconciled
The practical difficulty for most investors is not understanding the law: it is assembling a complete record. Every swap requires:
- The date and time of the transaction
- The sterling value of the token disposed of at that moment (from exchange data or a reliable price feed)
- The allowable cost, drawn from the correct s104 pool position at that point in time
- Correct application of the same-day and 30-day matching rules before the pool is touched
Exchange history exports give you the transaction data. Translating that into a legally correct UK CGT computation, across multiple wallets and exchanges and potentially thousands of transactions, is where DIY reconciliation most often goes wrong. US-default FIFO calculations, missing DeFi events, ignored same-day matches, and lost records from defunct exchanges are the most common errors seen in DIY returns.
Reconciliation tools such as Koinly or Recap can automate much of the data aggregation, but they require careful configuration for UK rules and manual review of edge cases. The output is a starting point for a UK CGT calculation, not a finished tax computation.
If your swap history runs to more than a handful of transactions, or if you have used DeFi protocols, multiple wallets, or received staking or mining rewards alongside your trading activity, the interactions between those different event types add complexity that a DIY approach is likely to miss. We work through the full picture, reconcile your history, and produce the correctly computed figures for your Self Assessment return. Visit our investor tax service or explore the reconciliation service to see how we approach the data.