# invest.section-104-pool **Status: needs review by a tax professional before it is published.** Works out the allowable cost of every disposal of one holding of shares under the UK share identification rules for individuals, for disposals on or after 6 April 2008. Give it every purchase and sale of one class of shares in one company, in date order and in sterling; it returns each day's disposal with the shares it was matched against, the proceeds and cost of each match, the gain or loss, and the Section 104 holding left at the end. ## The rules Each disposal is identified with acquisitions in this order: 1. **Same day.** Shares bought on the same day as the disposal (TCGA 1992 s105(1)(b)). All purchases on one day are one acquisition and all sales on one day are one disposal (s105(1)(a)), so the result has one disposal per day however many trades there were. 2. **The next 30 days** ("bed and breakfasting"). Shares bought in the 30 days after the disposal, earliest purchase first (s106A(5)). Day 30 counts; day 31 does not. Where two disposals could both claim one later purchase, the earlier disposal is matched first. 3. **The Section 104 holding.** Everything else comes out of the pool at its average cost (s104). Shares matched under 1 or 2 never enter the pool (CG51550). Same-day matching is settled for every day before any 30-day matching, so a purchase is taken by a sale on its own day before it can be claimed by an earlier sale's 30-day window. ## Rounding HMRC's own guidance apportions pool cost "by reference to the number of shares sold" (CG51575). Here the cost of a part of a purchase or of the pool is `cost left × shares taken / shares left`, rounded half-up to the penny, and taken from what is left, so the pieces always add back to the whole: selling the last share takes the last pennies. The day's proceeds are split across its matches the same way, so each match has its own gain or loss, as in the HS284 example. HMRC's worked examples use whole pounds; a reviewer should confirm the penny rounding. ## Edge cases and limits - A sale of more shares than are held at the end of that day is refused, even when a later purchase would be matched with it (a short sale). - Disposals before 6 April 2008 are refused: they followed different identification rules (and indexation). Purchases may be any date; for shares held on 31 March 1982, pass the purchase at its 31 March 1982 market value (CG51550). - Amounts are in GBP pence. Convert foreign-currency costs and proceeds at the rate on each transaction date before calling. - Out of scope: bonus and rights issues, reorganisations, takeovers, employee share schemes, the non-resident and trading-company variants of the 30-day rule (s106A(5A)), and the older "kink test". A buy's `amount` is its full allowable cost including dealing costs and stamp duty; a sell's is the proceeds after dealing costs. ## Sources Read on 2026-09-23: - HMRC Capital Gains Manual CG51550, "Shares and securities: identification rules: shares pooling from 6 April 2008": https://www.gov.uk/hmrc-internal-manuals/capital-gains-manual/cg51550 - CG51560, "Identification rules for individuals from 6 April 2008" (same day, then 30 days, then Section 104; TCGA92/S105(1), S106A(5) and (5A)): https://www.gov.uk/hmrc-internal-manuals/capital-gains-manual/cg51560 - CG51575, "Section 104 holding: part disposal" (apportion by number of shares): https://www.gov.uk/hmrc-internal-manuals/capital-gains-manual/cg51575 - CG51590, Example 1 (Ms Davy), used as a vector: https://www.gov.uk/hmrc-internal-manuals/capital-gains-manual/cg51590 - HS284 "Shares and Capital Gains Tax (2025)", Example 2 (Mr Schneider), used as a vector with a pool cost of our own (the helpsheet gives none): https://www.gov.uk/government/publications/shares-and-capital-gains-tax-hs284-self-assessment-helpsheet/hs284-shares-and-capital-gains-tax-2025 ## What a reviewer should check - Penny rounding of apportioned costs and proceeds. - That refusing short sales, rather than matching them with later purchases, is the right default. - The order of 30-day matching when several disposals and purchases overlap.