Cryptocurrency Capital Gains Tax Calculator 2025/26 — UK HMRC Rules

How HMRC Taxes Cryptocurrency in the UK

HMRC published its first guidance on the taxation of cryptoassets in 2018 and has updated it regularly since. The core position is clear: for most individuals, cryptocurrency is a capital asset, not a currency. This means the rules of Capital Gains Tax apply to every disposal — whether you sell for sterling, swap one cryptocurrency for another, use crypto to purchase goods or services, or give crypto away as a gift.

The 2025/26 CGT rates on crypto are 18% (for gains falling within the basic rate Income Tax band) and 24% (for gains above the basic rate limit). The annual exempt amount — the gains you can make each tax year before any CGT is due — is £3,000. This was dramatically cut from £12,300 in 2022/23 to £6,000 in 2023/24 and to £3,000 in 2024/25, meaning many more crypto holders are now within the CGT net.

What Counts as a "Disposal"?

This is the question most crypto investors misunderstand. HMRC's definition of a disposal is much broader than simply selling for pounds:

• Selling cryptocurrency for fiat currency (GBP, EUR, USD, etc.) — the obvious case
• Swapping one cryptocurrency for another — exchanging Bitcoin for Ethereum is a disposal of Bitcoin at its market value at the moment of the swap
• Using cryptocurrency to buy goods or services — paying for a product with Bitcoin triggers a CGT disposal
• Gifting cryptocurrency — except gifts to a spouse or civil partner, which are exempt and transfer the original cost base
• Receiving cryptocurrency as payment for work — this is actually income, not a capital gain, and is subject to Income Tax and NI at the value when received
• Airdrops and mining rewards — these are generally treated as income at the market value when received, with any subsequent gain on disposal being a capital gain
• DeFi transactions — lending, staking, and liquidity provision are complex areas; HMRC issued specific guidance in 2022 confirming that lending crypto may or may not be a disposal depending on whether beneficial ownership passes

HMRC's Section 104 Pool — How Your Cost Is Calculated

For most people, the most confusing aspect of crypto tax is working out the "allowable cost" (your base cost) when you have bought and sold the same cryptocurrency multiple times at different prices. HMRC uses the "section 104 pooling" rules, adapted from the share identification rules in TCGA 1992.

Under pooling, all acquisitions of the same cryptocurrency are averaged together into a single "pool." When you dispose of some of that cryptocurrency, the cost attributed to the disposal is the proportion of the total pool cost that corresponds to the proportion of the pool being sold. For example, if you bought 1 Bitcoin at £20,000 and another at £30,000, your pool contains 2 Bitcoin at an average cost of £25,000 each. Selling 1 Bitcoin would give you an allowable cost of £25,000.

The Same-Day Rule and 30-Day Rule

To prevent "bed and breakfasting" (selling to crystallise a loss and immediately rebuying), HMRC applies the same identification rules used for shares. If you buy and sell the same cryptocurrency on the same day, the buy and sell are matched against each other first — before the section 104 pool. Similarly, if you sell cryptocurrency and then buy more of the same type within the following 30 days, the sale is matched against those new acquisitions (at the new purchase cost) rather than the pool.

This 30-day rule is crucial for tax planning — it means you cannot effectively crystallise a loss for CGT purposes by selling and immediately rebuying. You must wait 30 days before rebuying if you want the loss to count against your gains.

Reporting Crypto Gains to HMRC

You must report capital gains from cryptocurrency to HMRC if your total gains in the tax year exceed the annual exempt amount (£3,000 in 2025/26), OR if your total proceeds from disposals exceed £50,000 (even if no tax is owed). Reporting is done through Self Assessment — either by completing the Capital Gains Tax supplementary pages of your Self Assessment tax return, or through the standalone "Report and pay Capital Gains Tax" service.

The deadline for reporting and paying CGT through Self Assessment is 31 January following the end of the tax year (so 31 January 2027 for the 2025/26 tax year). Unlike residential property (which requires a 60-day report), there is no separate in-year reporting obligation for crypto — though this may change in future.

Keeping Adequate Records

HMRC requires crypto investors to keep detailed records including: the date of every acquisition and disposal, the amount of each cryptocurrency involved, the value in sterling at the time of each transaction (using a consistent, reasonable valuation method — typically the market price at the time of the transaction), transaction fees, and any income received (staking rewards, mining income, airdrops). Many specialist crypto tax software tools (Koinly, CryptoTax Calculator, TaxBit, etc.) can import transaction data from exchanges and calculate your gains automatically.