If you’ve sold, swapped, or spent cryptocurrency in the UK, you almost certainly have a tax obligation — even if you never converted to pounds. HMRC treats crypto assets as a form of property, not currency, which means every disposal can trigger a capital gains event. Whether you made £500 or £50,000, understanding how to calculate your liability correctly can be the difference between filing accurately and facing penalties. This article walks through the exact HMRC rules for calculating crypto capital gains in the UK, including the Section 104 pooling method, the 30-day same-day rule, allowable costs, and what counts as a disposal in the first place.
How HMRC Classifies Crypto Assets
HMRC does not treat cryptocurrency as currency or money. According to HMRC’s own guidance document, CRYPTO10100 (Cryptoassets Manual), crypto assets are treated as a form of property for Capital Gains Tax (CGT) purposes. This classification has been in place since 2018 and was reaffirmed in updated guidance issued through 2024.
Most retail holders will be dealing with what HMRC calls exchange tokens — assets like Bitcoin and Ether used primarily as a store of value or medium of exchange. These are subject to CGT rules for individuals. Other categories, such as utility tokens and security tokens, may have different treatment, but CGT applies to the majority of everyday crypto transactions.
What Counts as a Disposal
A disposal is any event that triggers a capital gain or loss calculation. This is broader than most beginners expect. According to HMRC’s Cryptoassets Manual, the following all qualify as disposals:
- Selling cryptocurrency for pounds sterling or any other fiat currency
- Swapping one cryptocurrency for another (e.g. ETH for SOL)
- Using cryptocurrency to pay for goods or services
- Gifting cryptocurrency to someone other than a spouse or civil partner
- Donating crypto to a charity (though Gift Aid rules may apply)
Simply moving crypto between your own wallets is not a disposal, provided you can demonstrate both wallets belong to you. Receiving crypto as income — through mining, staking, or airdrops — is typically treated as income tax rather than CGT at the point of receipt, though a subsequent disposal of that crypto will trigger CGT.
The Section 104 Pool: How HMRC Calculates Your Cost Basis
The core method HMRC uses to identify the cost of crypto you’ve sold is the Section 104 pooling rule, drawn from the Taxation of Chargeable Gains Act 1992. Under this rule, all units of the same token you hold are pooled together into a single asset with a combined cost basis. Each time you acquire more, the pool grows; each time you dispose, you calculate a proportional share of the pool’s cost.
Worked Example
Suppose you bought 1 BTC for £10,000 in January, then another 1 BTC for £20,000 in June. Your Section 104 pool now contains 2 BTC at a total cost of £30,000 — an average cost of £15,000 per BTC. If you then sell 1 BTC for £25,000, your gain is £25,000 minus £15,000 = £10,000.
Each different token has its own separate pool. Your BTC pool is entirely separate from your ETH pool, your SOL pool, and so on.
The 30-Day Rule and Same-Day Rule
HMRC applies two anti-avoidance matching rules that take priority over the Section 104 pool. These exist to prevent “bed and breakfasting” — selling at a loss and immediately rebuying to manufacture a tax-deductible loss.
Same-Day Rule
If you buy and sell the same token on the same day, those acquisitions are matched first against any disposals on that same day, before consulting the pool.
30-Day Rule (Bed and Breakfasting)
If you sell a token and then repurchase the same token within 30 days, the repurchase is matched against the earlier sale — not added to the pool. This means you cannot realise a clean loss by selling and quickly rebuying. The 30-day rule applies in forward order: the buy after the sell is matched to the sell.
These matching rules must be applied in order: same-day first, then 30-day, then the Section 104 pool. Getting this order wrong is one of the most common mistakes in crypto tax calculations.
Allowable Costs You Can Deduct
You can reduce your capital gain by deducting certain allowable costs. According to HMRC’s Cryptoassets Manual, these include:
- The original acquisition cost of the crypto
- Transaction fees paid to acquire the crypto (e.g. gas fees, exchange fees)
- Transaction fees paid at the point of disposal
- Costs of drawing up contracts related to the transaction (rare in retail crypto)
Network fees (gas fees) paid when transferring between your own wallets are generally not deductible as an allowable cost against a gain, though HMRC’s guidance on this remains a point of interpretation. Subscription costs for portfolio tracking tools or tax software are also not deductible against CGT.
The Annual Exempt Amount and CGT Rates for 2025/26
Every UK individual has an Annual Exempt Amount (AEA) — a threshold below which capital gains are not taxed. For the 2025/26 tax year, this allowance stands at £3,000, following significant reductions from the £12,300 figure that applied before April 2023. HMRC reduced it to £6,000 in 2023/24, then to £3,000 from April 2024 onwards.
If your total net capital gains in the tax year exceed £3,000, the excess is taxed at the following rates (as updated in the October 2024 Autumn Budget):
- 18% — for gains falling within the basic rate income tax band
- 24% — for gains above the higher rate threshold
These rates replaced the previous 10%/20% crypto CGT rates from 30 October 2024. Your capital gains are added on top of your income for the purposes of determining which band applies.
Reporting Your Gains: Self Assessment
You must report capital gains from crypto through Self Assessment, even if no tax is owed, if your total proceeds from disposals exceed four times the Annual Exempt Amount (£12,000 for 2025/26), or if you have gains above the AEA. The deadline for online Self Assessment returns is 31 January following the end of the tax year (which runs 6 April to 5 April).
HMRC has also introduced a Real Time Transaction Service for reporting and paying CGT within 60 days in certain scenarios, though for crypto this typically applies to gains declared via the standard Self Assessment process rather than the 60-day property rule used for residential property.
Keep records of every transaction — date, amount in GBP at time of transaction, fees paid, and wallet addresses. HMRC can request records going back several years. Using dedicated crypto tax software (such as Koinly, CoinTracker, or TaxBit) that is explicitly aligned with HMRC’s Section 104 rules is strongly recommended, though you remain responsible for the accuracy of your return.
What This Means for You
The UK’s approach to crypto capital gains is rule-based and methodical — but it catches far more transactions than most holders realise. Swapping tokens on a DEX, paying for a service with ETH, or gifting crypto to a friend are all taxable events under current HMRC rules. The key practical steps are:
- Track every transaction from the moment you first acquire crypto, including wallet-to-wallet transfers for audit purposes
- Apply matching rules in the correct order: same-day, then 30-day, then Section 104
- Calculate gains in GBP using the exchange rate at the time of each transaction
- Deduct allowable acquisition and disposal costs before calculating the gain
- Check whether your net gains exceed the £3,000 AEA and file via Self Assessment if required
- Use the updated CGT rates of 18% and 24% for disposals made on or after 30 October 2024
HMRC has been actively issuing notices to crypto exchanges operating in the UK requesting customer data, so the assumption that crypto transactions are invisible to the tax authority is no longer tenable. Filing accurately and on time is the only realistic approach.
