HMRC treats cryptocurrency as a capital asset and applies share pooling rules (the Section 104 pool method) to calculate gains and losses. All units of the same cryptocurrency are held in a single pool. When you buy more, you add to the pool. When you sell, you remove units at the pool's average cost and the difference between proceeds and allowable cost is your gain or loss.
This calculator lets you enter your starting pool position and add Buy and Sell transactions one by one. It maintains a running pool, shows each transaction's gain or loss, and produces a final CGT summary including the annual exempt amount (£3,000 for 2025/26).
HMRC Crypto Matching Order
- Same-day rule: Match disposals with same-day acquisitions first.
- 30-day rule (bed and breakfast): Match with acquisitions within the following 30 days next.
- Section 104 pool: Any remaining disposals are matched against the pool at average cost.
- This calculator uses Section 104 pool matching only. Apply same-day and 30-day rules manually before using this tool if relevant.
Section 104 Pool Calculator
Step 1: Starting Pool Position
Step 2: Add a Transaction
Pool quantity: 0 coins | Pool total cost: £0 | Average cost per coin: £0
| # | Type | Qty | Price (£) | Proceeds/Cost | Allowable Cost | Gain / Loss | Pool Qty After | Pool Cost After |
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This calculator implements Section 104 pool matching only. Apply same-day and 30-day (bed and breakfast) rules before entering sells where those rules may apply. Annual exempt amount 2025/26: £3,000. Not tax advice.
Understanding the Section 104 Pool
The Section 104 pool is named after Section 104 of the Taxation of Chargeable Gains Act 1992 (TCGA). It treats all units of the same cryptocurrency held by an individual as a single pool of assets. Rather than identifying which specific coins are being sold, HMRC requires you to calculate a weighted average cost across the entire pool and apply that average to each disposal.
This method prevents investors from selectively choosing which "lot" of coins to sell to minimise gains. For example, if you bought 1 BTC at £10,000 and later 1 BTC at £40,000, your pool of 2 BTC has a total cost of £50,000 and an average cost of £25,000 per coin. If you then sell 1 BTC, the allowable cost is £25,000 regardless of which purchase you consider yourself to be selling.
Every buy transaction increases the pool quantity and pool cost. Every sell transaction reduces both in proportion. The pool never goes below zero.
The Same-Day Rule and 30-Day Rule
HMRC applies two priority matching rules before the Section 104 pool. The same-day rule matches any disposal with acquisitions of the same cryptocurrency on the same day. This prevents investors from inflating their average pool cost artificially by buying and selling on the same day.
The 30-day rule (sometimes called the bed and breakfast rule) matches a disposal with acquisitions of the same cryptocurrency made within the following 30 calendar days. This prevents investors from selling to crystallise a loss and then immediately buying back to refresh their pool cost. If you sold Bitcoin at a loss on 1 March and rebought Bitcoin on 20 March, the 1 March sale is matched with the 20 March purchase at the repurchase price, not the pool average cost. The loss may be reduced or eliminated as a result.
Both rules must be applied in order before resorting to the Section 104 pool. If your trading pattern includes rapid buy-sell cycles or strategic loss harvesting followed by repurchase, you should apply these rules manually before using this calculator.
Reporting Crypto Gains to HMRC
Crypto disposals must be reported on a Self Assessment tax return (SA108 Capital Gains pages). You must report all disposals in the tax year, including crypto-to-crypto swaps (treating each swap as a disposal at market value). If you have not previously submitted a Self Assessment return, you may need to register for one if your total proceeds exceed £50,000 or your net gains exceed the annual exempt amount (£3,000 for 2025/26).
HMRC has increasingly strong data on crypto holdings through exchange reporting requirements and its own data collection programmes. Investors who have not declared past crypto gains should consider making a voluntary disclosure. HMRC has published a Cryptoassets Manual with detailed technical guidance on all aspects of cryptocurrency taxation including DeFi, staking, and NFTs.
Frequently Asked Questions
What is the Section 104 pool for cryptocurrency?
HMRC treats cryptocurrency like shares and applies the Section 104 pooling method. All units of the same cryptocurrency are pooled. Each purchase adds units and cost to the pool. Each sale removes units at the pool's average cost per unit, and the gain or loss is the difference between proceeds and the allowable cost removed from the pool.
How does the Section 104 pool calculation work?
On each buy, add quantity and total cost to the pool. Pool average cost = total pool cost / total pool quantity. On each sell, allowable cost = (quantity sold / pool quantity before sale) × pool cost before sale. Gain = proceeds − allowable cost. Then reduce pool quantity and cost by the amounts used.
What is the same-day rule for crypto?
If you buy and sell the same cryptocurrency on the same day, the disposal is matched first with the same-day acquisition before using the Section 104 pool. This prevents artificial manipulation of the pool average cost.
What is the 30-day bed and breakfast rule for crypto?
If you sell cryptocurrency and buy the same cryptocurrency within 30 days afterwards, the disposal is matched with those later purchases rather than the Section 104 pool. This prevents crystallising losses and immediately re-buying to refresh cost base.
What is the CGT annual exempt amount for 2025/26?
The annual exempt amount for 2025/26 is £3,000. Net gains up to this amount are free from CGT. Gains above the threshold are taxed at 18% (basic rate) or 24% (higher rate) for non-residential assets including crypto.
Do I need to report crypto gains below the exempt amount?
If total proceeds from all crypto disposals exceed four times the annual exempt amount (£50,000 in 2025/26), you must report on Self Assessment even if no tax is due. You must also report if net gains exceed £3,000. Always keep full records.
Is staking or mining income subject to CGT?
Staking rewards and mining income are generally treated as miscellaneous income when received. When you later sell those tokens, CGT applies with the market value at time of receipt as the cost base. Occasional or non-commercial activity may be treated differently.
Is a crypto-to-crypto swap a CGT event?
Yes. Swapping one cryptocurrency for another is a disposal for CGT purposes. You dispose of the original coin at its sterling market value at the time of the swap and acquire the new coin at the same sterling value as its cost base. Each swap generates a separate CGT event.
Can I offset crypto losses against other capital gains?
Yes. Crypto losses can be offset against any other capital gains in the same tax year. If losses exceed all gains, the excess is carried forward to future years indefinitely.
What records should I keep for crypto CGT?
Keep records of: cryptocurrency type, date of each transaction, quantity bought or sold, sterling value at transaction date, cumulative pool cost and quantity, and transaction fees. Records must be kept for at least 5 years after the filing deadline for the relevant tax year.
Does the Section 104 pool apply to NFTs?
No. NFTs are unique and cannot be pooled with identical items. Each NFT has its own acquisition cost and disposal proceeds. Section 104 applies only to fungible tokens where each unit is identical.
What CGT rate applies to crypto gains in 2025/26?
Cryptocurrency gains are taxed at 18% for basic rate taxpayers and 24% for higher and additional rate taxpayers in 2025/26. These are the same rates as for shares and other non-residential capital assets.