The 30-Day 'Bed and Breakfasting' Rule for Crypto: How HMRC Stops Wash Sales

In December every year, UK crypto traders look at their loss-making positions and think the same thing: "If I sell now and re-buy tomorrow I can crystallise a loss to offset my gains." HMRC's 30-day rule — sometimes called the "bed and breakfasting" rule, after a now-banned practice of doing the same trick with shares — is what stops you. It is the single most misunderstood part of UK crypto tax.

The matching order HMRC requires

When you dispose of a token, HMRC matches the disposal against acquisitions in this fixed order: first, any acquisitions of the same token on the same day (the "same-day rule"); second, any acquisitions in the next 30 days (the "30-day rule"); finally, against your Section 104 pool average cost. Only what is left over after rules one and two falls back to the pool.

The 30-day rule applies even if the re-buy happens after the disposal — the matching looks forward in time, not just backward.

Worked example: memecoin loss harvest

You bought 10,000,000 PEPE for £6,000 in April. By December it is worth £2,000 and you have £8,000 of crypto gains you want to offset. You sell all 10m PEPE for £2,000, intending to claim a £4,000 loss. The next morning you buy 10m PEPE back at the same price.

Under the 30-day rule, your December disposal is matched against your December re-purchase, not against your April Section 104 pool. The result: a tiny gain or loss based purely on the price difference between the sell and the re-buy (likely £0). Your April cost basis stays in the pool for next time. You did not crystallise a loss.

What still works

Selling and not re-buying for 31+ days. The matching gap is closed and the disposal goes against the Section 104 pool, producing the loss you wanted.

Selling token A and buying a different token B (a different cryptocurrency, not a re-wrap of the same thing). HMRC has not extended a "substantially identical" wash-sale concept the way the US has, so disposing of ETH and buying SOL is a clean disposal — although disposing of WETH and re-buying ETH the same week probably is a same-asset matching.

Selling and gifting to a spouse who then re-buys (interspousal transfers do not trigger CGT and are not matched, so the 30-day rule does not apply across spouses).

Stablecoin pairs

Swapping USDC for USDT and back within 30 days creates a forward-and-back match that nets to roughly zero. That is fine — you neither gain nor lose anything material — but it does still produce two reported disposals on your Self Assessment.

What this means in practice

Loss harvesting in UK crypto needs at least a 31-day window between the sell and the re-buy. Plan it before the tax year ends (5 April), not after. The 2025/26 window has already closed; for 2026/27 you have until early March 2027 to sell and avoid the re-buy until the tax year resets.

CryptoLens applies same-day, 30-day and Section 104 matching automatically against every wallet you scan, so you can see the actual loss available before committing to a sale.