CGT on Shares Calculator

Working out capital gains tax on shares starts with the cost side, and the rules do not let you choose which shares you sold. Under section 104 of TCGA 1992, every share of the same class in the same company is pooled together and carries a single average cost. When you sell, the gain is the sale proceeds less that average cost multiplied by the number of shares disposed of, then less allowable expenses such as broker commission and the stamp duty paid on purchase.

Two matching rules jump the queue ahead of the pool. Anything sold is first matched against shares of the same type bought on the same day. Whatever is left is then matched against purchases made in the following 30 days, the rule usually called bed and breakfasting, which exists to stop people crystallising a loss by selling and immediately buying the same holding back. Only once both have been applied does the section 104 pool come into play. Most brokers do not track the pool for you, which is why specialist software such as CGT Sheets or Sharesight tends to fill the gap.

The first £3,000 of gains in a tax year is covered by the annual exempt amount. Above that, gains falling within your basic-rate band are taxed at 18% and gains above it at 24%, the rates that have applied since 30 October 2024. Because gains stack on top of income, a single disposal can straddle the threshold, with the slice that pushes you past the basic-rate limit taxed at the higher figure. Selling 500 shares with a pooled cost of £10 each for £18 each produces a £9,000 receipt, a £4,000 gain, £1,000 of taxable gain after the exemption and £240 of tax at 24%.

A disposal covers more than a straightforward sale, since transferring shares counts too, with transfers to a spouse or to charity the main exceptions. The standard planning move is bed and ISA: selling a holding outside an ISA, using up the annual exempt amount on the gain, then buying it straight back inside the wrapper so future growth sits beyond the reach of tax.

Employee share schemes run on their own rules. Shares from an EMI arrangement can qualify for Business Asset Disposal Relief once the option was granted at least two years before the sale, with no 5% shareholding needed, which taxes the gain at 18% from 6 April 2026 (14% in 2025/26) instead of the 24% higher rate. SAYE and Sharesave shares are bought at a discount and can be moved into an ISA within 90 days for continuing shelter. Shares left in a Share Incentive Plan trust for 5 years attract neither income tax nor CGT, and a Company Share Option Plan avoids income tax where the options are held for at least 3 years.

Losses are the part people forget to claim. A loss on one disposal offsets gains made in the same tax year, so a profitable sale can be netted against a poor one before the exemption is applied. Anything unused carries forward indefinitely against future gains, but only if you claim it within 4 years of the end of the tax year in which the loss arose, through Self Assessment. Paper losses on holdings you still own do not count, however grim the valuation looks, because only realised disposals register.