UK Crypto CGT Calculator · guide

Section 104 pooling for crypto: a worked UK example

If you bought Bitcoin more than once, HMRC does not let you say which coins you sold. It treats all your units of one cryptoasset as a single pool and, before touching the pool, checks two shorter rules. This page works one example in pounds. The calculator runs the same arithmetic on your own file.

The order HMRC matches a disposal

1. Same day. Units of the same asset you bought on the day you sold.
2. The next 30 days. Units you bought in the 30 days after the sale, earliest first. This stops you selling to claim a loss and buying straight back.
3. The Section 104 pool. Everything else comes out of one pool at its average allowable cost.

The example

All numbers are invented. Fees are in pounds. A fee on a purchase adds to its cost; a fee on a sale comes off the proceeds.

The pool before 2024. 0.8 BTC at a cost of £15,020 + £10,515 = £25,535.

2 May 2024. You sold 0.4 BTC for £19,200 less a £25 fee: £19,175, or £47,937.50 a coin. You also bought 0.1 BTC the same day for £6,210 including the fee. So the same-day rule matches 0.1 BTC: proceeds £4,793.75 against cost £6,210, a loss of £1,416.25. The other 0.3 BTC comes from the pool at £25,535 × 0.3 ÷ 0.8 = £9,575.625, against proceeds of £14,381.25, a gain of £4,805.63 (to the penny). The pool is left with 0.5 BTC at £15,959.375. The 0.1 BTC you bought that day never entered the pool.

11 Nov 2024. You sold 0.2 BTC for £13,982 after the fee. You buy 0.15 BTC back on 25 Nov, 14 days later, for £10,212. The 30-day rule matches that 0.15 BTC: proceeds £10,486.50, cost £10,212, a gain of £274.50. The last 0.05 BTC comes from the pool at £15,959.375 × 0.05 ÷ 0.5 = £1,595.94, against proceeds of £3,495.50, a gain of £1,899.56. The bought-back coins are used up and also never enter the pool, which is left with 0.45 BTC at £14,363.44.

Adding it up for 2024-25

The year runs 6 April 2024 to 5 April 2025. In this file the BTC disposals produce gains of £6,979.69 and a loss of £1,416.25; the calculator's sample file adds an ETH-to-SOL swap and a SOL sale for a fuller picture. The annual exempt amount for 2024-25 is £3,000. Gains above it were taxed at 10% or 20% for disposals up to 29 October 2024 and 18% or 24% from 30 October 2024, depending on how much of your basic-rate band your income leaves free.

Where people go wrong

• Treating each sale as first-in first-out. HMRC's pool is an average, so an old cheap coin does not sit under a new sale.
• Selling and rebuying within 30 days. The loss you expect is replaced by a match against the repurchase.
• Forgetting swaps. Swapping one coin for another is a disposal, at the pound value of what you received.
• Missing purchases. A sale with no matching purchase has no cost, so the gain looks far too large. The calculator warns when that happens.