The 30-Day Bed and Breakfast Rule for Crypto: A Worked Example

The 30-day rule — sometimes called the "bed and breakfast" rule from the equivalent share rule — is the piece of UK tax legislation that most crypto sellers get wrong. Sell a coin at a loss on Monday, rebuy the same coin on Wednesday, and you have not crystallised the loss for CGT purposes. Here is exactly how the matching rules under TCGA 1992 s.106A work for crypto, with a fully worked BTC example.

The three matching rules, in order

When you dispose of a crypto asset, HMRC identifies the acquisition that matches the disposal in this strict order:

1. **Same-day rule (s.105 TCGA 1992):** any acquisition of the same asset on the same day matches first. 2. **30-day / bed-and-breakfast rule (s.106A TCGA 1992):** any acquisition of the same asset within the 30 days after the disposal matches second, on a first-in-first-out basis. 3. **Section 104 pool:** everything else matches against the pooled cost basis.

You do not get to pick. The order is mandatory. If you had a same-day buy and a 20-day-later buy, the same-day buy is matched first.

The 30-day window is calendar days, not trading days. The count starts the day after the disposal.

Why the rule exists

Without it, you could sell BTC at a loss to crystallise a deduction, then immediately buy it back and be economically identical. HMRC would have handed you a tax deduction for a fictitious loss. The 30-day rule forces the "rebuy" to replace the cost basis of the "sell", so the two cancel out for CGT until you actually break the position for more than 30 days.

Worked example: BTC across three matching layers

Let's build a realistic year of trades and see the matching.

**January 2026:** buy 1 BTC at £30,000. Section 104 pool: 1 BTC, cost £30,000.

**April 2026:** buy 1 BTC at £40,000. Pool: 2 BTC, cost £70,000 total, £35,000 average.

**5 September 2026:** BTC hits £60,000 and you want to bank the gain. Sell 1 BTC at £60,000.

**8 September 2026 (3 days later):** BTC dips to £45,000 and you buy 1 BTC back.

Now apply the matching rules to the 5 September disposal.

- Same-day: no acquisitions on 5 September. Skip. - 30-day window (6 September to 5 October): the 8 September buy at £45,000 falls in this window. Match it against the disposal. - The 5 September disposal is now matched to the 8 September acquisition, not to the Section 104 pool.

Gain on the disposal: £60,000 proceeds minus £45,000 cost = **£15,000 gain**.

Section 104 pool is unchanged: still 2 BTC at £70,000 (the 5 September disposal took nothing from the pool, and the 8 September acquisition was consumed by the matching).

Compare with the naïve S104-only calculation: £60,000 minus £35,000 average = £25,000 gain. The matching rule gave you a lower gain because you effectively repurchased cheaper — but only because your rebuy was actually cheaper than the pool average. If you had rebought at £50,000, the matched gain would have been £10,000; the pool answer would have been £25,000.

Worked example: the loss case where the rule bites

The rule most often bites in reverse — a loss-harvesting attempt that fails.

- 1 January 2026: buy 1 BTC at £60,000. Section 104 pool: 1 BTC, £60,000. - 1 December 2026: BTC has dropped to £30,000. You sell 1 BTC to "harvest" a £30,000 loss. - 5 December 2026: BTC has bounced to £35,000 and you buy 1 BTC back to maintain the position.

Matching the 1 December disposal:

- Same-day: none. - 30-day: the 5 December buy at £35,000 is in the window. Match to the disposal. - Loss on the disposal: £30,000 proceeds minus £35,000 cost = **£5,000 loss**.

You wanted to crystallise a £30,000 loss; the rule limited you to a £5,000 loss. The Section 104 pool is unchanged at 1 BTC, £60,000 cost.

If instead you had waited 31 days before rebuying, the disposal would have matched against the Section 104 pool: £30,000 proceeds minus £60,000 cost = £30,000 loss. The Section 104 pool would then be empty at the moment of your later rebuy, and the later rebuy would start a new pool at £35,000 (or whatever the 31st-day price was).

This is exactly why the CryptoLens <a href="/loss-harvest">loss harvest tool</a> flags the 30-day window explicitly — if you plan to harvest a loss, you must stay out of the market for the whole window.

Same-asset means same-asset

The rule applies to the same crypto asset. Selling BTC and buying WBTC is a different asset (per HMRC's wrapper guidance in CRYPTO22050 — they are separate cryptoassets for CGT). Similarly, ETH and stETH are different assets. So you can, in theory, sell BTC and buy WBTC within 30 days without triggering the matching — but you are then exposed to the wrapper being un-pegged, and any subsequent unwind is its own disposal.

Do not attempt this without an accountant sign-off. HMRC could still challenge as a Ramsay/Bright Line arrangement if the pattern is obviously artificial.

Same-day rule quirk

The same-day rule matches the total same-day acquisitions to the total same-day disposals on a pooled basis for that day, not trade-by-trade. If you bought 0.3 BTC and sold 0.5 BTC on the same day, the 0.3 BTC bought pools with the disposal for that portion; the remaining 0.2 BTC disposal then falls to the 30-day rule or the S104 pool.

Common misconceptions

- **"I sold on one exchange and rebought on another, so the rule does not apply."** Wrong. The rule applies to the asset, not the venue. Selling on Coinbase and buying on Binance within 30 days still matches. - **"I sold ETH and bought BTC, so the loss is real."** Correct on the ETH loss — but any ETH bought back within 30 days would trigger the matching. - **"The rule only applies to shares."** Wrong. TCGA 1992 s.106A applies to any chargeable asset within the pooling regime, including crypto per HMRC CRYPTO22200. - **"I can just move to a spouse's account and rebuy from there."** The rule follows the taxpayer, not the wallet. A spouse buying within 30 days does not trigger your matching (they are a separate taxpayer), but see <a href="/blog/crypto-spouse-transfer-tax-uk">spouse transfers</a> for the more general planning.

Filing pipeline

1. Import all your wallets and exchanges via <a href="/import">/import</a>. 2. On <a href="/tax">/tax</a>, review each disposal — CryptoLens applies same-day, 30-day, then Section 104 pool matching automatically per s.106A. 3. Sanity-check any disposal near a rebuy — the tool shows which acquisition was matched. 4. Use <a href="/loss-harvest">/loss-harvest</a> before 5 April 2027 to plan any loss crystallisation without falling into the 30-day trap.