# UK crypto CGT worked example — pooling and a swap explained

Example: buy 1 BTC at £20,000 and 1 BTC at £40,000 (pool average £30,000). Sell 1 BTC for £50,000 → gain £20,000 before allowance. Swapping BTC for ETH is a disposal at sterling market value — same maths. Deduct the £3,000 annual exempt amount if no other gains.

## Key facts
- Each token type has its own pool.
- Swaps are disposals even without cash.
- Fees reduce proceeds or add to cost.
- Losses in the same year offset gains.
- Use our CGT calculator to model your figures.

## Example 1 — Two purchases, one sale

April 2025: buy 0.5 BTC for £15,000 (£30,000 per BTC). August 2025: buy 0.5 BTC for £25,000 (£50,000 per BTC). Pool: 1 BTC costing £40,000 — average £40,000 per BTC. March 2026: sell 1 BTC for £55,000. Gain = £55,000 − £40,000 = £15,000. After £3,000 annual exempt amount, taxable gain £12,000. At 18% basic / 24% higher rate on crypto gains depending on your income band.
## Example 2 — Swap BTC for ETH

You dispose of BTC at sterling value on swap day. If 0.2 BTC worth £12,000 is swapped for ETH, BTC pool cost is deducted (pro-rata from pool). You acquire a new ETH pool at £12,000. No cash changes hands but CGT still applies on any BTC gain.
## Example 3 — 30-day rule

You sell 1 ETH on 1 June for £3,000 (pool cost £2,000, gain £1,000). You buy 1 ETH back on 15 June for £2,800. The 30-day rule matches the sale to the rebuy — adjusting gain calculation before the pool. HMRC applies same-day rule first, then 30-day, then Section 104 pool.
## Putting figures on SA108

Sum all disposal proceeds for the tax year → box 13.2. Sum allowable costs → 13.3. Net gains → 13.4. Losses → 13.5. See our SA108 guide for the full checklist.

## FAQs
### Do I use the price on the exchange or HMRC rate?

Use a consistent sterling market price at transaction time. Many filers use exchange prices; HMRC publishes rates for some conversions.

## Sources

- [HMRC — Cryptoassets Manual](https://www.gov.uk/hmrc-internal-manuals/cryptoassets-manual)
- [HMRC — Capital Gains Tax rates](https://www.gov.uk/capital-gains-tax/rates)

---

— Digital Assets UK (https://digital-assets.co.uk/tax/cgt-worked-example-uk/), reviewed 2026-06-23. Source: https://www.gov.uk/hmrc-internal-manuals/cryptoassets-manual