capital gains tax calculator uk shares

How this capital gains tax calculator for UK shares works

This page is designed to help you quickly estimate Capital Gains Tax on a share sale. You enter your sale proceeds, your allowable cost base, your losses, and your taxable income for the year. The calculator then applies:

• Your gain before tax reliefs
• Any capital losses you want to offset
• Your remaining Annual Exempt Amount (AEA)
• The basic-rate and higher-rate CGT split for shares

The result gives you a practical estimate of your CGT bill and a full breakdown so you can see where the number comes from.

Inputs you should gather before calculating

1) Sale proceeds

This is your gross amount received when you sold the shares.

2) Purchase cost and allowable costs

Use your original acquisition cost plus valid dealing costs. For UK shares, many investors include:

• Broker commission on purchase
• Stamp Duty Reserve Tax (where relevant)
• Broker commission on sale

3) Capital losses

Losses from other disposals can often be used to reduce gains. Use losses that are available and claimable for the same tax year (or brought forward losses already reported to HMRC).

4) Taxable income

Your taxable income affects which part of your gain falls into the lower CGT rate band versus the higher rate band. If your income already uses up the basic-rate band, most or all taxable gain is charged at the higher CGT rate.

Worked example (quick)

Suppose you sell shares for £25,000 with a total cost base (purchase + fees) of £15,500. You also have £1,000 of usable losses, and £3,000 AEA remaining.

• Gain before losses: £25,000 - £15,500 = £9,500
• After losses: £9,500 - £1,000 = £8,500
• After AEA: £8,500 - £3,000 = £5,500 taxable gain

The tax then depends on your unused basic-rate band and the applicable CGT rates for shares in your tax year.

Key HMRC rules that can change your real gain

Share matching order matters

For UK CGT, share disposals are not always matched simply to your oldest purchase. HMRC matching rules generally consider:

• Same-day acquisitions first
• Acquisitions within 30 days (the “bed and breakfast” rule)
• Then your Section 104 holding (pooled cost)

Because of this, your true allowable cost can be very different from a simple average. For accurate returns, calculate your matched cost from full transaction history.

Corporate actions

Events like rights issues, share splits, takeovers, and demergers can alter your pooled cost and acquisition records. Keep contract notes and broker statements safely stored.

Ways investors reduce mistakes

• Download annual tax reports from each broker
• Track every buy/sell fee, not just headline prices
• Record losses promptly and claim where required
• Check how much of your AEA is already used elsewhere
• Run scenarios before year-end to manage disposals

Frequently asked questions

Does this calculator include dividends?

No. Dividends are separate from capital gains and taxed under dividend tax rules.

Can I use it for funds and ETFs?

It can give a rough estimate, but fund disposals may involve separate details and reporting nuances. Always verify cost matching and fund records.

Is ISA share disposal taxable?

Disposals inside an ISA are generally free of UK CGT. This calculator is mainly for taxable (non-ISA, non-pension) share accounts.

Final note

If you were searching for a capital gains tax calculator uk shares tool that is easy to use and clear, this page should help you estimate quickly and understand the mechanics. Use it for planning, then confirm with your own records before submitting your Self Assessment return.