Capital Gains Tax Calculator for UK Shares
Calculate your capital gains tax liability when selling shares in the UK. This calculator considers your purchase price, selling price, associated costs, and your annual tax-free allowance.
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Capital Gains Tax Due
How to Use This Calculator
How Capital Gains Tax Works on UK Shares
When you sell shares for more than you paid, the profit is called a capital gain. You might need to pay Capital Gains Tax on this gain, but only after deducting allowable costs and your annual tax-free allowance.
The Calculation Process
First, work out your gain by subtracting what you paid (including costs) from what you received (minus selling costs). Then deduct your annual CGT allowance, which is £3,000 for the 2025/2026 tax year. Any remaining gain is taxable.
The rate you pay depends on your income tax band. Basic rate taxpayers pay 18% on gains from shares and investments, while higher and additional rate taxpayers pay 24%. These rates changed from 10% and 20% respectively from April 2025.
What Costs Can You Deduct?
You can deduct several costs from your gain:
- Stockbroker fees and commission
- Stamp Duty Reserve Tax (0.5% on purchases)
- Platform charges directly related to buying or selling
- Professional advice costs for the transaction
Share Pooling Rules
If you’ve bought the same shares at different times, you can’t just match each sale with a specific purchase. Instead, UK tax rules require you to use share pooling. All shares of the same type in the same company are pooled together, and the average cost is used when calculating gains.
There are special ordering rules though. Shares sold are matched in this order: same day acquisitions first, then acquisitions within the next 30 days, and finally the share pool.
Ways to Reduce Your CGT Bill
Use Your ISA Allowance
Shares held in a Stocks and Shares ISA are completely exempt from CGT. You can invest up to £20,000 per tax year. Consider transferring shares into your ISA allowance, though you may trigger a gain when doing so.
Transfer to Your Spouse
Transfers between married couples or civil partners are CGT-free. Your spouse can then use their own £3,000 allowance. This effectively doubles your combined tax-free amount to £6,000.
Offset Losses
Capital losses from selling shares at a loss can offset gains. Report losses to HMRC within four years. They can be carried forward indefinitely to reduce future gains.
Time Your Sales
Spreading sales across tax years lets you use multiple years’ allowances. The tax year runs from 6 April to 5 April. Careful timing can significantly reduce your tax bill.
Pension Contributions
Making pension contributions reduces your income, potentially moving you from higher rate to basic rate. This cuts your CGT rate from 24% to 18% on gains.
Use Your SIPP
Self-Invested Personal Pensions are free from CGT on investments held within them. You also get tax relief on contributions up to your annual allowance.
CGT Rates and Allowances
| Tax Year | Annual Allowance | Basic Rate | Higher/Additional Rate |
|---|---|---|---|
| 2025/2026 | £3,000 | 18% | 24% |
| 2024/2025 | £3,000 | 10% | 20% |
| 2023/2024 | £6,000 | 10% | 20% |
| 2022/2023 | £12,300 | 10% | 20% |
Frequently Asked Questions
You must report gains on shares in a Self Assessment tax return for the tax year in which you sold them. The deadline is 31 January following the end of the tax year. For example, if you sold shares in July 2025, you’d report this by 31 January 2027.
No, you don’t pay CGT on gains below your annual allowance. However, if your total proceeds from all asset sales exceed four times the annual allowance (£12,000), you must still report this to HMRC, even if no tax is due.
Losses can reduce your capital gains in the same tax year. If your losses exceed your gains, you can carry the unused losses forward to reduce gains in future years. You must report losses to HMRC within four years of the end of the tax year.
No. Shares held in a Stocks and Shares ISA are completely exempt from Capital Gains Tax, no matter how large your gain. This makes ISAs incredibly tax-efficient for long-term investing.
If you buy the same shares within 30 days of selling them, you can’t use the loss to reduce your capital gains. This anti-avoidance rule prevents “bed and breakfasting” – selling to create a loss then immediately buying back.
No, dividends aren’t subject to CGT. They’re treated as income and subject to dividend tax instead. You have a separate dividend allowance of £500 for 2025/26. Dividend tax rates are different from CGT rates.
When you inherit shares, your base cost for CGT purposes is their market value at the date of death. You don’t pay CGT on inheriting them, only when you eventually sell them. If you don’t know the Inheritance Tax value, you should use the market value.
Only costs directly related to buying or selling specific shares are deductible. Annual platform fees or account charges cannot be deducted. Transaction-specific charges like dealing fees and stamp duty can be deducted.
Common Mistakes to Avoid
Forgetting to Report Small Gains
Even if your gain is below the £3,000 allowance, you must report it if your total proceeds from all disposals exceed £12,000 in the tax year. Many people miss this requirement and face penalties.
Not Keeping Proper Records
You need evidence of purchase prices, dates, costs, and selling prices. Keep contract notes, bank statements, and platform statements for at least six years after the tax year. Without these, HMRC may estimate your gain unfavourably.
Ignoring Share Pooling Rules
You can’t choose which shares you’re selling if you bought the same company’s shares at different times. The share pooling rules dictate the cost basis. Many investors incorrectly calculate gains by matching specific purchases to sales.
Missing the Reporting Deadline
Late filing penalties start at £100 and increase the longer you delay. If tax is owed, interest accrues from 31 January. Set reminders and file early to avoid unnecessary costs.
Not Claiming Allowable Losses
Losses must be reported within four tax years or you lose them forever. Even if you don’t have gains to offset, report losses so you can carry them forward. This is particularly valuable as allowances have reduced.
Assuming All Costs Are Deductible
Only costs directly incurred in buying or selling are allowable. Research costs, subscription services, and financial advice not specific to a transaction cannot be deducted from your gain.
Tax-Efficient Investing Strategies
Smart planning can dramatically reduce your CGT liability over time. Here’s how experienced investors structure their portfolios:
Maximise Tax-Sheltered Accounts First
Always fill your £20,000 ISA allowance before investing in a general investment account. Combine this with pension contributions for maximum tax efficiency. A couple can shelter £40,000 per year in ISAs alone.
Harvest Losses Strategically
Review your portfolio before each tax year end. Selling investments at a loss can create valuable tax relief. You can then reinvest in similar (but not identical) assets to maintain your investment strategy whilst reducing tax.
Use the Bed and ISA Strategy
Sell shares in your general account and immediately buy them back in your ISA. This uses your CGT allowance whilst moving assets into a tax-free wrapper. You can do this each year to gradually shelter your portfolio.
Consider Timing of Sales
If you’re planning a large sale, spreading it across multiple tax years can utilise multiple years’ allowances. Selling £6,000 over two years uses two £3,000 allowances rather than one.