UK Capital Gains Tax, 2026/27

Section 104 share pooling, step by step

Selling shares you bought or vested at different times is not simple averaging. HMRC matches each sale to your acquisitions in a fixed order. This shows the order on your own numbers.

Enter one share class only -- e.g. one employer’s RSUs. Pooling mixes every acquisition’s cost together, so adding shares from a different company or a different class produces a meaningless blended average.

Acquisitions

Every time you got these shares: RSU vests (cost = vest-date value) or purchases.

Acquisition 1 date

Falls in tax year 2024/25

Price per share

Acquisition 2 date

Falls in tax year 2026/27

Price per share

Acquisition 3 date

Falls in tax year 2026/27

Price per share

Disposals

Every time you sold them.

Disposal 1 date

Falls in tax year 2026/27

Price per share

Taxable income above your personal allowance

From salary and other income, used to split the gain between the 18% and 24% CGT rates

Matching order, disposal by disposal

Disposal 1: 500 shares on 2026-06-01

200 shares matched same-day
150 shares matched via the 30-day bed-and-breakfast rule
150 shares matched from the Section 104 pool

Proceeds £12,500 − allowable cost £8,800 = gain £3,700

Result

Total gain: £3,700
Annual exempt amount used: £3,000
CGT owed: £168
Section 104 pool remaining: 850 shares, £8,500 pooled cost

The matching order, in priority

When you dispose of shares, HMRC does not let you choose which specific shares you’re selling, and it is not a simple running average either. The cost used against each sale is found by matching it to your acquisitions in a fixed priority order (TCGA 1992, HMRC helpsheet HS284):

Same-day rule. Matched first to any acquisitions made on the exact same day as the disposal.
30-day bed-and-breakfast rule. Anything left over is matched next to acquisitions in the following 30 days, earliest first. This exists specifically to stop selling and immediately rebuying the same shares from resetting your cost base.
Section 104 pool. Whatever remains draws on a single pooled holding, whose cost is the running average of every acquisition not already matched by the first two rules.

For RSUs, the acquisition cost of each tranche is its value on the vest date, since that value was already taxed as employment income. Capital Gains Tax then only applies to growth above that value.

This tool models pooling for a single sale or a single share class in isolation. For the full vest-to-sale flow, including the income tax at vest and a sell-versus-hold comparison, use the full RSU + CGT planner.

This is a generic illustration. It is not financial, tax, or investment advice and does not account for your full circumstances.