If you are selling shares or other investments, you may incur Capital Gains Tax (CGT) on any profit, or 'gain', you make. You will need to work out your gain to determine if you need to pay tax, which depends on whether your total gains exceed your CGT allowance for the tax year. 

You usually pay CGT on total gains above your annual tax-free allowance, which is currently £3,000. If your gains exceed the allowance, you must report and pay CGT. This is usually done through self-assessment, with different reporting deadlines depending on the type of asset disposed of. The rate of tax depends on your income. Basic rate taxpayers pay 18% CGT on gains within the basic rate band and 24% on amounts above it. Higher and additional rate taxpayers generally pay 24% CGT on all gains.

You do not usually pay CGT when you give shares as a gift to your husband, wife, civil partner, or a charity. Additionally, shares including those held within an ISA, those in employer Share Incentive Plans (SIPs) and UK government gilts are exempt. Your gain is typically the difference between what you paid for your shares and the sales proceeds. 

You can deduct costs like stockbrokers' fees and Stamp Duty Reserve Tax (SDRT) from your gain. Various tax reliefs may also reduce or delay your CGT liability, including Business Asset Disposal Relief, Gift Hold-Over Relief, Enterprise Investment Scheme (EIS), Seed Enterprise Investment Scheme (SEIS), and Rollover relief. Special rules apply for working out the cost of shares bought at different times in the same company, or if sold through an investment club.

It is important to calculate your gain, consider any applicable reliefs, and report to HMRC if your total gains exceed the annual allowance.