The 30-day rule (section 105 TCGA 1992) prevents CGT loss harvesting via "bed-and-breakfasting" — selling shares to crystallise a loss, then immediately buying them back. If you re-buy the same asset within 30 calendar days, HMRC matches the disposal with the new purchase, not the section 104 pool. The result: the loss disappears, replaced by an adjusted cost basis on the new purchase. The rule applies to all CGT assets, not just shares: crypto, art, property all subject. Workarounds: wait 31 days, buy a different but correlated asset, or use a spouse's account.
The mechanic
When you sell a CGT asset, HMRC normally matches the disposal with the section 104 pool (your average cost basis). The 30-day rule changes that:
- If you re-buy the same asset within 30 days, HMRC matches the disposal with the new purchase first, then the pool.
- The matched portion uses the new purchase price as its cost — not the pool average.
- The "loss" (or gain) on the matched portion is calculated against the new purchase price.
- Result: a sale-then-rebuy at a similar price has near-zero gain/loss, and the pool's existing cost basis is preserved for future disposals.
This blocks the standard wash-sale loss-harvesting technique.
Worked example
Loss-harvesting attempt blocked by the rule
| You hold 1,000 shares of XYZ Ltd in section 104 pool, average cost £10 | £10,000 |
| XYZ price drops to £6/share. You sell all 1,000 to crystallise £4,000 loss | −£4,000 |
| Next day (still under 30-day window), you buy 1,000 XYZ shares at £6 | £6,000 |
| HMRC matches the disposal with the new £6 purchase | |
| Disposal proceeds £6,000 − new cost £6,000 = nil gain/loss on matched portion | £0 |
| The original pool of 1,000 shares at £10 average remains intact, but cost basis becomes £6 |
The £4,000 loss is functionally disallowed for CGT purposes. The pool's cost basis is now £6/share (the new purchase price), which means future disposals at £10 would crystallise a £4,000 gain — the loss has been "deferred" rather than denied. But you can't use it this year.
Three legitimate workarounds
1. Wait 31+ days
The cleanest workaround. Sell, wait at least 31 days (some safety margin advisable), then re-buy. The 30-day rule no longer applies; the disposal is matched against the section 104 pool, and the loss is properly crystallised.
Risk: market movement during the 31-day window. If the asset rises, you've missed the recovery. If it falls further, you can re-buy at an even lower price (good for you).
2. Bed and ISA
Sell from your General Investment Account, immediately buy the same asset inside your ISA. The disposal crystallises CGT (using the pool basis); the new purchase is inside the ISA wrapper. The 30-day rule technically applies, but practically the loss harvesting still works because the new purchase isn't a personal CGT asset anymore — gain/loss inside ISA is irrelevant.
See Bed-and-ISA for the mechanism.
3. Bed and Spouse
Sell from your account, your spouse buys the same asset in their account within 30 days. Spousal transfers are CGT-exempt; the spouse's acquisition becomes their cost basis (not yours). The 30-day rule technically applies to the same individual — so a spouse purchase doesn't trigger the rule for you. The loss in your account stands.
Note: HMRC may challenge if there's clear "beneficial ownership" gaming — if the spouse purchase is purely a wash-trade with no genuine economic substance. Document the timeline and the spouse's actual control of the purchased asset.
The "different but correlated" workaround
Instead of selling and re-buying the same fund, sell Fund A and buy Fund B (similar but not identical exposure). Examples:
- Sell Vanguard FTSE All-World UCITS ETF (VWRL), buy iShares Core MSCI World UCITS ETF (SWDA). Both global equity but different index providers.
- Sell Vanguard S&P 500 (VUSA), buy Invesco S&P 500 (SPXS).
The two funds aren't "the same asset" for the 30-day rule, so it doesn't apply. Your exposure is materially similar; the loss is properly crystallised.
Caveat: HMRC has occasionally argued that two ETFs tracking the same index are "the same asset" for the rule. Tribunal cases are sparse but generally allow the workaround for distinct funds with different providers. Specialist advice for large amounts.
Same-day rule (the other matching rule)
Separate from the 30-day rule: if you buy AND sell the same asset on the same day, the disposal is matched with the same-day purchase first (before the 30-day rule even gets considered). This is rarely an issue for retail investors — it mainly affects day traders.
How the rule applies to crypto, property, art
- Crypto: The 30-day rule applies to crypto. Selling and re-buying within 30 days disallows the loss. Pooling is by asset (BTC pool, ETH pool, etc.). Workaround: wait 31 days or swap to a different cryptocurrency.
- Property: The rule applies in theory but is rarely an issue — property sales don't typically have 30-day round trips.
- Art / collectibles: Same as property — the practical issue is rare.
Sources and methodology
The 30-day rule is in section 105 of the Taxation of Chargeable Gains Act 1992. CGT rates and pooling rules follow HMRC's CGT guidance. For specific positions involving complex pooling, derivative wrappers, or international assets, see the tax adviser recommendation. The methodology page documents sources.
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