Calculating the capital gain on the sale of an investment

When you sell an investment—whether that’s shares, property, or other assets—you may need to pay Capital Gains Tax (CGT). Understanding how to calculate this liability is crucial for planning ahead and avoiding any unwelcome surprises from HMRC. In this guide, we’ll walk through the calculation process and highlight the thresholds and rates you need to know for the 2024/25 tax year.

What is a Capital Gain?

A capital gain is simply the profit you make when you sell an asset for more than you paid for it. The calculation sounds straightforward: selling price minus the original cost. However, HMRC allows you to adjust this figure for certain costs incurred during ownership, such as professional fees, improvements to the asset, or costs directly related to buying or selling it.

For example, if you purchased shares for £5,000 and sold them for £8,000, your gross gain is £3,000. However, if you paid £200 in professional fees and £150 in dealing charges, your allowable costs total £5,350, reducing your gain to £2,650.

The Annual Exemption and Who Pays CGT

The good news is that not all capital gains are taxable. For the 2024/25 tax year, individuals have an annual CGT exemption of £3,000. This means you only pay tax on gains above this threshold.

However, it’s important to note that companies don’t benefit from this exemption—they pay Corporation Tax on all gains. Additionally, higher rates apply if you’re resident outside the UK or if the gains relate to UK residential properties, where special rules apply.

For individuals, once your gains exceed £3,000, you’ll pay tax at one of two rates, depending on your income tax band. Basic rate taxpayers pay 10% on most gains, whilst higher and additional rate taxpayers pay 20%. For residential property gains (other than your main residence), the rates are higher: 18% and 24% respectively.

Working Out Your Tax Bill

Let’s break down the calculation step by step.

Step 1: Identify allowable costs. These include the original purchase price, acquisition costs (stamp duty, legal fees), and enhancement costs (improvements that add lasting value). Maintenance and repairs don’t count—only capital improvements do.

Step 2: Calculate the gain. Subtract total allowable costs from your sale proceeds.

Step 3: Deduct the annual exemption. If your total gains for the year are under £3,000, you pay nothing. If they exceed this, only the surplus is taxable.

Step 4: Apply the appropriate tax rate. Check your income tax position. If you’ve used up your basic rate band with employment income, gains may be taxed at the higher rate. Capital gains sit “on top” of your other income for tax purposes.

For instance, if you’re a basic rate taxpayer with £5,000 in gains, you’d calculate: (£5,000 − £3,000 exemption) × 10% = £200 tax due.

Timing and Reporting

You’re required to report capital gains on your Self Assessment tax return, even if you don’t owe any tax. This is crucial—failure to notify HMRC can result in penalties. If you’re required to file a Self Assessment return, gains should be reported by 31 January following the tax year in which the sale occurred.

For property sales, additional rules apply. Non-resident landlords and some property disposals trigger mandatory reporting requirements, and HMRC may collect tax at source through the property sale proceeds.

Claiming Losses and Relief

One final consideration: if you’ve made losses on other investments, you can offset these against gains to reduce your tax bill. Capital losses can only be used against capital gains, not against income, but they can be carried forward indefinitely to use in future years. Make sure you keep detailed records of both gains and losses—they may prove invaluable at tax time.

Conclusion

Calculating CGT needn’t be daunting, but it does require attention to detail and accurate record-keeping. Getting your figures right at the outset will save you time and stress later on. If you’re unsure about any aspect of your tax position—whether you’ve correctly identified allowable costs, worked out your exemption correctly, or simply want to review your overall tax strategy—professional advice is always worthwhile.

For tailored advice, contact Severn Accounting — we’re here to help.