How to calculate crypto taxes in the UK (2026 HMRC guide)

Calculating UK crypto tax is not hard, but it is unforgiving. HMRC uses a specific share-pooling regime with three matching rules in a fixed order, and getting that order wrong is the single most common reason a Self Assessment figure ends up either too high or too low. This guide walks through the calculation method in 2026, with a worked example you can follow line by line.

How HMRC taxes crypto

HMRC treats crypto as a chargeable asset for Capital Gains Tax. A taxable disposal happens when you sell for fiat, swap one token for another, spend crypto on goods or services, or gift crypto to anyone other than your spouse or civil partner. For each disposal you compute a gain or loss as proceeds minus allowable costs, sum them across the tax year, deduct the annual exempt amount, and pay CGT on the rest.

Allowable costs include the original purchase price, exchange fees, transaction (gas) fees on the buy and sell sides, and a fair share of pooled-asset costs under Section 104 of the Taxation of Chargeable Gains Act 1992. The tax year runs from 6 April to 5 April; for 2025/26 the deadline to file online is 31 January 2027.

The three matching rules

When you dispose of a crypto asset, HMRC asks: which acquisition is being sold? The answer is determined by three matching rules applied in this order.

1. Same-day rule. If you bought the same asset on the same day as the disposal, the disposal is matched against that purchase first, in chronological order if there are several.
2. 30-day (bed-and-breakfasting) rule. If you bought the same asset in the 30 days after the disposal, the disposal is matched against those purchases on a first-in-first-out basis. This blocks the classic trick of selling at a loss and re-buying immediately.
3. Section 104 pool. Anything left over is matched against the pool — a single weighted average cost basis covering every other unit of that asset you have ever bought.

Section 104 share pool

The pool is the heart of UK crypto tax. Imagine a single bucket per asset (one for BTC, one for ETH, one for SOL, and so on). Every acquisition that does not get consumed by the same-day or 30-day rule goes into the bucket. The pool tracks two numbers: total quantity and total allowable cost. When you dispose of pool units, you take a proportional slice of the cost out with you.

Worked example: you buy 1 BTC for £20,000 in May, then 1 BTC for £30,000 in July. The pool is now 2 BTC with £50,000 of cost — an average of £25,000 per coin. If you later sell 0.5 BTC for £18,000, the allowable cost taken from the pool is 0.5 × £25,000 = £12,500. The gain is £18,000 − £12,500 = £5,500. The pool is left with 1.5 BTC and £37,500 of cost.

Worked example: 5 disposals across a tax year

Here is a complete 2025/26 example. Five transactions, three matching rules, one final CGT figure.

We process disposal #3 (sell 4 ETH for £14,000) using the rules in order.

1. Same-day rule. 1 ETH was bought on 15 September at £3,400. Match 1 ETH of the disposal against this. Proceeds for that 1 ETH = £14,000 × 1/4 = £3,500. Cost = £3,400. Gain = £100.
2. 30-day rule. 2 ETH were bought on 10 October, within 30 days of the 15 September sale. Match 2 ETH of the disposal against these. Proceeds = £14,000 × 2/4 = £7,000. Cost = £7,200. Loss = −£200.
3. Section 104 pool. The remaining 1 ETH comes from the pool. Before the disposal the pool held 15 ETH at £35,000 (10 at £20,000 + 5 at £15,000) — an average of £2,333.33 per ETH. Proceeds for that 1 ETH = £14,000 × 1/4 = £3,500. Cost = £2,333.33. Gain = £1,166.67.

Net gain on disposal #3: £100 − £200 + £1,166.67 = £1,066.67. Pool after the transaction: 14 ETH at £32,666.67 of cost.

CGT rates and allowance for 2026

The 2025/26 numbers, which carry into the 2026 tax cycle:

• Annual exempt amount (AEA): £3,000. The first £3,000 of net gains is tax-free.
• Basic-rate CGT: 18%. Applies to gains that fall within your remaining basic-rate band.
• Higher-rate CGT: 24%. Applies to gains above the basic-rate threshold.

Because the rates are stacked on top of your other income, you have to know your taxable salary, dividends and rental income before you know which rate applies. The official position is set out at gov.uk Capital Gains Tax rates.

When crypto is income, not CGT

Some crypto activity is taxed as miscellaneous income, not CGT, and shows up on a different part of the return. The most common income events are:

• Staking rewards — valued in £ at the spot price on the day received.
• Mining rewards (whether hobby or trade — the test is your level of organisation and effort).
• Lending interest from CeFi or DeFi protocols.
• Airdrops where you have done something to earn them (community tasks, referrals).

Each receipt also sets the cost basis for the eventual disposal. If you later sell the staked ETH, your cost is the £ value on the day it was credited to you.

Shortcuts and tools

Doing share-pooling by hand for fewer than 30 transactions is feasible. Beyond that — particularly with DeFi swaps, bridges and re-staking — most filers reach for software. We compare the leading options in our UK crypto tax software roundup, and walk through a full Self Assessment in our step-by-step reporting guide. For loss claims specifically, see claiming UK crypto losses.

Whatever method you use, keep the workings: HMRC can ask to see your matching schedule for up to four years (six if they suspect carelessness, twenty if they suspect deliberate concealment).