Crypto Record-Keeping for CGT: What HMRC Actually Expects in 2026/27

Quick answer

For Capital Gains Tax purposes, HMRC expects UK crypto investors to keep a full transaction history for every disposal — not just cash-outs to a bank account — including the date, the type of asset, the nature of the transaction (sale, swap, gift, spend), its sterling value at the time, and supporting evidence such as exchange statements or blockchain transaction IDs. Good records are the difference between a straightforward Self Assessment return and a stressful reconstruction exercise years later.

Swaps count as disposals, even without a cash-out

One of the most commonly missed points is that swapping one cryptoasset for another — say, exchanging one token for a different one directly — is treated by HMRC as a disposal of the first asset and a fresh acquisition of the second, both valued in pounds sterling at the time of the swap. This means a taxable gain can arise even though the investor never withdrew any money to a bank account, which catches out anyone who assumes tax only becomes relevant once crypto is converted back to cash.

How pooling works

Rather than tracking the exact original cost of each individual token, HMRC applies a pooling approach: tokens of the same type held by the same person are treated as a single pool with an averaged cost per token, updated as tokens are bought and sold. Specific matching rules apply for transactions on the same day, and for transactions within 30 days of a disposal, which is designed to prevent artificial "bed and breakfasting" of gains and losses. Keeping a running pooled-cost spreadsheet, or using software that applies these rules correctly, is far more reliable than manually tracking individual purchase prices.

When exchanges disappear

Crypto exchanges close, get hacked, or simply stop providing historical statements — but the responsibility for maintaining adequate records for tax purposes stays with the individual taxpayer, not the exchange. Where original exchange data is missing, HMRC still expects a reasonable, evidenced reconstruction, using whatever combination of wallet addresses, blockchain explorer data, bank statements showing fiat deposits and withdrawals, and personal records (spreadsheets, screenshots, emails) is available.

Software helps, but doesn't replace judgement

Crypto tax software can automate a large proportion of the pooling and gain/loss calculation work by importing exchange and wallet data directly, which is a significant time-saver for anyone with hundreds of transactions. But import errors, unsupported transaction types (particularly staking rewards, liquidity pool activity, and cross-chain bridges), and duplicated transfers between a user's own wallets are common sources of incorrect output, so spot-checking a sample of the software's calculations against the raw data is still worthwhile before relying on the final figure.

Bottom line

Treat every crypto transaction — not just cash withdrawals — as a potential taxable event, keep contemporaneous sterling-value records as transactions happen rather than trying to reconstruct them at tax return time, and don't assume a disappeared exchange removes the record-keeping obligation.

Sources

• HMRC: Cryptoassets Manual
• gov.uk: Check if you need to pay tax when you sell cryptoassets