CGT Share Pooling Calculator (Section 104)

The Section 104 pool (or 'pool') is the standard HMRC method for calculating CGT on shares. It pools all purchases of the same class of shares in a company, tracking the total number of shares and total cost.

When you buy shares, the cost is added to the pool. The 'average cost per share' is the total pool cost divided by total shares. When you sell, the gain is calculated using this average cost.

If you sell shares and buy the same shares back within 30 days (bed and breakfast), HMRC matches the sale to the repurchase price — not the Section 104 pool — to prevent artificial loss creation.

Any shares bought on the same day as a sale are matched to that sale first, before the 30-day rule or Section 104 pool.

The matching rules apply to UK-resident individuals disposing of quoted shares. Different rules may apply to shares in unquoted companies or to non-residents.

Shares acquired through SAYE, SIPs, EMI, and CSOP have specific identification rules. Generally they follow the same Section 104 principles but there may be special provisions.

A share split or consolidation changes the number of shares in the pool but not the total cost. The average cost per share adjusts proportionately.

Shares acquired through dividend reinvestment are added to the Section 104 pool at the price on the reinvestment date, like a normal purchase.

No. HMRC does not allow FIFO for shares. The Section 104 pool (average cost) method must be used, subject to the same-day and 30-day matching rules.

Keep records of every purchase and sale: date, number of shares, price per share, and any costs (broker commissions, stamp duty). HMRC recommends keeping records for at least 4 years.

Yes. Unit trusts and OEICs are treated like shares for CGT purposes. The Section 104 pool applies to accumulation and income units/shares of the same class.

Shares in an ISA are completely separate — they're not part of your Section 104 pool and any gains/losses within the ISA are exempt from CGT.