Section 104 Pooling Explained for Investment Clubs

What is a Section 104 pool?

A Section 104 pool (named after Section 104 of the Taxation of Chargeable Gains Act 1992) is a running record of the total quantity and total cost of all shares of a particular company that the club has ever bought. When shares are sold, the gain is calculated against the average cost per share in the pool.

Every time the club buys more shares in a company, the quantity and cost are added to the pool. The pool grows over time and the average cost per share changes with each new purchase.

A simple example

After the sale, the pool is reduced: 600 shares remaining, £787.50 total cost. The average cost stays the same.

The matching rules: same-day and 30-day come first

Before consulting the Section 104 pool, HMRC applies two anti-avoidance rules. Both are designed to prevent artificial loss creation.

1. Same-day matching

If the club buys and sells shares in the same company on the same day, those transactions are matched directly against each other — regardless of the pool. The gain or loss is calculated from the actual prices paid that day.

2. The 30-day rule (bed and breakfasting)

If the club sells shares and then buys shares in the same company within 30 days of the sale, the sale is matched against the repurchase — not the pool. This is the so-called "bed and breakfast" rule.

It exists because otherwise a club could sell shares to crystallise a loss, claim the loss against other gains, then immediately buy back in at the same price — effectively manufacturing a tax deduction for free.

The matching priority order

1. Same-day purchases — matched first
2. Purchases within 30 days after the sale — matched second (earliest purchase date first)
3. Section 104 pool — everything else goes here

Only the quantity not absorbed by rules 1 and 2 falls through to the pool calculation. This ordering matters: if the club sells 500 shares and bought 200 the next day, only 300 shares use the pool cost.

How this affects each member

Once the club-level gain is calculated, it's allocated to each member based on their ownership percentage at the time of the sale. A member who owned 15% of the club at the point of sale has realised 15% of that gain — regardless of how much they contributed historically.

This per-member allocation is what each member reports on their self-assessment, subject to their own Annual Exempt Amount and other CGT positions.

What can go wrong

• Forgetting to apply the 30-day rule — the most common error. Results in understated gains or overstated losses.
• Mixing up tax years — the UK tax year runs April 6 to April 5. Transactions on April 5 and April 6 are in different tax years.
• Using purchase price instead of pool average — if you're tracking lots individually (like a broker statement), you may be using FIFO instead of the UK-required pool average.
• Forgetting bonus shares and rights issues — these add to the pool at zero cost (bonus) or at the subscription price (rights), and the pool total must be updated accordingly.