The same-day rule for crypto disposals
Under the same-day rule, if you sell a token and also buy more of the same token on the same calendar day, the sale is matched against that day's purchases first — before the 30-day rule or the Section 104 pool. Where there are several purchases on the day, their cost is pooled and apportioned by quantity, so your cost basis is the same-day average. This rule exists to stop same-day churning from distorting your gain.
Why the rule exists
Without it, you could sell tokens from a cheap old pool and immediately buy them back the same day, crystallising an artificial gain or loss while your actual position never changed. The same-day rule closes that door: same-day buys and sells of the same token are matched to each other first, whatever order they happened in during the day.
How matching works
Take everything you acquired of that token on the calendar day of the disposal. If you disposed of less than you acquired, the disposal matches entirely at the day's (blended) acquisition cost, and the surplus acquisition goes on into the 30-day check and then the pool. If you disposed of more, the same-day portion matches first and the remainder falls through to the next rules.
Multiple same-day buys are treated as one blended lot: their costs are combined and apportioned by quantity, so the matched cost is the day's average — you can't cherry-pick the most favourable same-day purchase.
Example
You hold 100 SOL in your pool at an average cost of £50. On 12 May you sell 30 SOL at £90 each (£2,700) and, later the same day, buy 10 SOL at £88 each (£880).
- Same-day: 10 of the 30 sold match the same-day buy → proceeds £900, cost £880, gain £20
- The remaining 20 fall to the pool (no purchases in the next 30 days): proceeds £1,800, cost 20 × £50 = £1,000, gain £800
- Total gain: £820 — not the £1,200 a naive pool-only calculation would give
Run your own numbers — free
Our calculator applies these rules to your transactions and shows the full working for every disposal — same-day, 30-day and Section 104 matching, per tax year.
Open the calculator →Frequently asked questions
Does the time of day matter?
No. The rule works on the calendar day. A buy at 09:00 and a sell at 23:00 on the same date are matched, regardless of order.
Does the same-day rule apply across different exchanges?
Yes. It's per token per day, not per platform. A sale on one exchange matches a purchase of the same token on another exchange the same day.
What if I buy more than I sell on the day?
The sale is fully matched at the day's average acquisition cost. The unmatched surplus of the purchase is then available to the 30-day rule (for earlier disposals) or enters your Section 104 pool.
Sources & methodology
- HMRC Cryptoassets Manual CRYPTO22200 — pooling and the same-day / 30-day identification rules
- HMRC Cryptoassets Manual
Tool v0.2.0 · sources last checked 6 July 2026. This guide is general information, not tax or financial advice — verify your position with a qualified professional before filing.