How to Calculate Crypto Tax in the UK (2025/26 Guide)

If you have sold, swapped, or spent cryptocurrency in the UK, you probably owe Capital Gains Tax (CGT). HMRC treats crypto as property, not currency, which means every disposal is a taxable event. This guide walks you through exactly how to calculate what you owe for the 2025/26 tax year.

What counts as a taxable disposal?

HMRC considers any of the following a disposal: selling crypto for GBP or another fiat currency, swapping one token for another (including stablecoin conversions), spending crypto on goods or services, and gifting crypto to someone other than your spouse or civil partner. Simply holding or transferring between your own wallets is not a taxable event.

The CGT allowance

Every UK taxpayer gets a Capital Gains Tax-free allowance. For the 2025/26 tax year this is £3,000 — significantly lower than the £12,300 it was just a few years ago. Only gains above this threshold are taxed. Basic-rate taxpayers pay 18% on crypto gains, while higher-rate taxpayers pay 24%.

How to calculate your gain

For each disposal you need two numbers: the cost basis (what you originally paid, including fees) and the proceeds (what you received). Your gain is simply proceeds minus cost basis. HMRC requires you to use share-pooling rules rather than tracking individual coins. This means you calculate a weighted average cost for each token across all your purchases, then use that average to determine the gain on each sale.

Same-day and 30-day rules

Before applying share-pooling, HMRC requires two matching rules. The same-day rule: if you buy and sell the same token on the same day, those transactions are matched first. The 30-day rule (also called the "bed and breakfasting" rule): if you sell a token and re-buy it within 30 days, the sale is matched against the re-purchase rather than the pool. These rules are designed to prevent people from selling and immediately re-buying just to realise a loss.

Allowable deductions

You can deduct reasonable costs from your gains, including exchange trading fees, gas fees for on-chain transactions, and the GBP cost of transferring funds to an exchange. You cannot deduct the cost of hardware wallets, internet access, or general research time.

Reporting to HMRC

If your total crypto disposals exceed four times the annual allowance (£12,000 for 2025/26) or you have gains above the allowance, you must report them on a Self Assessment tax return. You can report via the online portal or by paper return. The deadline for online returns is 31 January following the end of the tax year.

Common mistakes to avoid

Many people forget that token-to-token swaps are taxable — swapping ETH for SOL triggers a disposal of ETH. Others forget to include DeFi transactions, liquidity pool entries and exits, or airdrops (which are taxed as income at the point of receipt). Keeping detailed records throughout the year makes the process far easier.

Calculating crypto tax manually is tedious, especially if you have hundreds of transactions across multiple wallets and exchanges. CryptoLens automates the entire process — connect your wallets and get your UK tax summary in seconds.