Crypto-to-Crypto Swap Tax UK: Why HMRC Treats Every Trade as a Disposal
Token-to-token swaps trigger Capital Gains Tax in the UK, even with no GBP movement. How HMRC values the trade, the matching rules, and the swaps UK traders most commonly miss.
The single most expensive UK crypto tax misconception is that you only owe tax when you cash out to GBP. You do not. HMRC treats every token-to-token swap as a disposal of the first token and an acquisition of the second, regardless of whether any pound sterling ever touches your bank account. This guide is the short, no-nonsense version of what that means at filing time.
The rule
HMRC guidance at CG12100 and CRYPTO22150 is unambiguous: a swap of crypto-asset A for crypto-asset B is a chargeable disposal of A. The proceeds of the disposal equal the GBP market value of B at the moment of the swap. Your gain is that GBP value minus the Section 104 pool average cost of A.
How HMRC values the swap
The proceeds figure is the GBP value of whatever you received at the block timestamp of the swap. For an ETH-to-USDC swap on Uniswap at 14:32 on a given day, HMRC wants the spot GBP value of the USDC you received at 14:32 — pulled from CoinGecko, the exchange feed, or any reasonable price source. Tools that use end-of-day prices are technically slightly wrong; the precise figure is the block-time price.
What this catches
Common UK trader activity that triggers CGT without GBP movement: swapping ETH for SOL on a CEX, swapping USDC for a memecoin on Uniswap, wrapping ETH to wETH (yes, this is a disposal — see HMRC's "different rights and obligations" test), unwrapping wstETH back to ETH, providing or withdrawing liquidity from an AMM pool, and bridging one token across chains via a contract that mints a different representation.
What does NOT count as a disposal
Moving the same token between your own wallets is not a disposal. Sending BTC from your Coinbase account to your Ledger is not a disposal. Approving a token on an exchange or DEX is not a disposal. Holding through a chain upgrade where the token is treated as the same asset (e.g. ETH through the Merge) is not a disposal. A pure rebrand or 1:1 contract migration is usually not a disposal but is fact-dependent.
Matching rules apply
Once the disposal is identified, HMRC applies same-day matching first (same-day acquisitions of the same token), then the 30-day "bed and breakfasting" rule (acquisitions in the 30 days following the disposal), then the Section 104 pool. The same matching rules apply to every swap, not just fiat sales.
Why this matters more in 2026
CARF reporting from January 2026 means UK-supervised exchanges send transaction-level data to HMRC. The gross volume on your exchange account is visible. If your Self Assessment shows three £10,000 fiat sales but the exchange reported £200,000 of token movements, the discrepancy is exactly the unfiled crypto-to-crypto swaps. The risk of "if I do not cash out, they will not know" is materially higher now than it was even 12 months ago.
A single wallet scan with CryptoLens enumerates every disposal — including every swap — into one SA108 row per event, with the correct GBP value at the block timestamp and the matching method already applied.
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