How Do You Calculate Capital Gains Tax On Shares

Calculate your potential capital gains tax liability when selling shares in the UK

Understanding how to calculate capital gains tax (CGT) on shares is essential for UK investors to optimise their tax position and avoid unexpected liabilities. This comprehensive guide explains the calculation process, current tax rates, allowances, and strategies to minimise your CGT bill when selling shares.

What is Capital Gains Tax on Shares?

Capital Gains Tax is a tax on the profit you make when you sell (or ‘dispose of’) shares that have increased in value. You only pay tax on the gain – not the total amount you receive from the sale. The tax applies to:

• Shares in companies (not held in ISAs or PEPs)
• Unit trusts and investment funds
• Government gilts and corporate bonds
• Cryptocurrencies (treated as assets for CGT purposes)

How to Calculate Your Capital Gain

The basic calculation for capital gains is:

Capital Gain = Sale Proceeds – Purchase Cost – Allowable Expenses

1. Determine Your Sale Proceeds

This is the total amount you receive from selling your shares, minus any selling costs like broker fees or stamp duty.

2. Calculate Your Purchase Cost

This includes:

• The original price you paid for the shares
• Purchase commission or broker fees
• Stamp duty (0.5% for UK shares)
• Any enhancement expenditure (e.g., costs that increase the value of the shares)

3. Bed and Breakfasting Rules (30-Day Rule)

HMRC’s anti-avoidance rules prevent you from selling shares to crystallise a loss, then buying them back immediately. If you repurchase the same shares within 30 days, the original cost is used for CGT calculations rather than the repurchase price.

Current Capital Gains Tax Rates (2023-24)

The CGT rates depend on your income tax band and the type of asset:

Income Tax Band	CGT Rate (Shares)	CGT Rate (Property)
Basic rate (£12,571 to £50,270)	10%	18%
Higher rate (£50,271 to £125,140)	20%	28%
Additional rate (over £125,140)	20%	28%

Note: These rates apply to gains above your annual exempt amount (see below).

Annual Exempt Amount (CGT Allowance)

Each tax year, you have an annual exempt amount (also called the CGT allowance) which has changed significantly in recent years:

Tax Year	Annual Exempt Amount
2023-24	£6,000
2024-25 (proposed)	£3,000
2022-23	£12,300
2021-22	£12,300

You only pay CGT on gains above this allowance. Married couples and civil partners can combine their allowances by transferring assets between them.

Step-by-Step Calculation Example

Let’s work through a practical example to illustrate how to calculate CGT on shares:

1. Purchase Details: You bought 1,000 shares in Company X at £10 per share in 2020, paying £10,000 plus £50 broker fee and £50 stamp duty (0.5%). Total cost = £10,100.
2. Sale Details: You sell all shares in 2023 for £18 per share, receiving £18,000 minus £90 broker fee. Net proceeds = £17,910.
3. Calculate Gain: £17,910 (proceeds) – £10,100 (cost) = £7,810 gain.
4. Apply Allowance: Subtract £6,000 (2023-24 allowance) = £1,810 taxable gain.
5. Determine Rate: If you’re a higher-rate taxpayer, you’ll pay 20% on the £1,810.
6. Calculate Tax: £1,810 × 20% = £362 CGT due.

Special Cases and Exemptions

1. Shares in ISAs and PEPs

You don’t pay CGT on shares held in:

• Individual Savings Accounts (ISAs)
• Personal Equity Plans (PEPs)
• Junior ISAs
• Lifetime ISAs (for qualifying withdrawals)

2. Employee Share Schemes

Special rules apply to shares acquired through:

• Company Share Option Plans (CSOPs)
• Save As You Earn (SAYE) schemes
• Share Incentive Plans (SIPs)
• Enterprise Management Incentives (EMIs)

Gains on these shares may qualify for CGT relief or different tax treatment.

3. Business Asset Disposal Relief (Formerly Entrepreneurs’ Relief)

If you’re selling shares in your personal company, you might qualify for Business Asset Disposal Relief, which reduces the CGT rate to 10% on the first £1 million of qualifying gains over your lifetime.

4. Investors’ Relief

For external investors in unlisted companies, Investors’ Relief offers a 10% CGT rate on gains up to £10 million (lifetime limit), provided you’ve held the shares for at least 3 years.

How to Reduce Your Capital Gains Tax Bill

1. Use Your Annual Allowance

Time your disposals to use your annual CGT allowance each tax year. For couples, transferring assets between spouses can double the allowance.

2. Offset Capital Losses

Capital losses can be offset against gains in the same tax year or carried forward to future years. You must report losses to HMRC within 4 years of the end of the tax year when you disposed of the asset.

3. Bed and ISA

Sell shares to realise a gain, then repurchase them within an ISA wrapper. This crystallises the gain (using your allowance) while sheltering future growth from CGT.

4. Bed and Spouse

Transfer shares to your spouse (tax-free) before selling. This can utilise both partners’ CGT allowances and potentially lower the tax rate if one partner pays a lower income tax rate.

5. Invest in EIS or SEIS

Investments in Enterprise Investment Schemes (EIS) or Seed Enterprise Investment Schemes (SEIS) can defer CGT liabilities or provide income tax relief.

6. Gift Shares to Charity

Donating shares to charity is CGT-free and may qualify for income tax relief on the value of the shares.

Reporting and Paying Capital Gains Tax

When to Report

You must report and pay any CGT due on UK residential property within 60 days of completion. For other assets (including shares), you report gains through your Self Assessment tax return by 31 January following the end of the tax year.

How to Report

1. Register for Self Assessment if you’re not already registered
2. Complete the capital gains pages of your tax return (SA108)
3. Calculate your gain using HMRC’s official guidance
4. Submit your return and pay any tax due by 31 January

Record Keeping

HMRC requires you to keep records for at least 5 years after the 31 January submission deadline. Records should include:

• Purchase and sale contracts
• Broker statements
• Receipts for costs (fees, stamp duty, etc.)
• Calculations of gains or losses
• Details of any reliefs claimed

Common Mistakes to Avoid

• Forgetting to include all costs: Many investors only consider the purchase price and sale price, forgetting to include broker fees, stamp duty, and other allowable expenses.
• Ignoring the 30-day rule: Selling and repurchasing the same shares within 30 days can trigger the bed and breakfasting rules.
• Not using losses: Failing to offset capital losses against gains means paying more tax than necessary.
• Missing deadlines: Late reporting can result in penalties and interest charges.
• Incorrectly calculating partial disposals: When selling only part of a shareholding, you must use the correct method (usually the ‘section 104 holding’ rules) to calculate the cost basis.

Capital Gains Tax for Non-UK Residents

Non-UK residents are generally only liable for CGT on:

• UK residential property
• UK commercial property (since April 2019)
• Shares in property-rich companies (where 75%+ of value comes from UK land)

Non-residents have the same annual exempt amount as UK residents but may have different reporting requirements. The GOV.UK website provides detailed guidance for non-residents.

Recent Changes and Future Outlook

The CGT landscape has seen significant changes in recent years:

• 2020-21: The annual exempt amount was frozen at £12,300 until 2026
• 2023-24: The allowance was halved to £6,000
• 2024-25: The allowance is proposed to halve again to £3,000
• 2023: The higher rate for residential property was reduced from 28% to 24% (though shares remain at 20%)

Future changes may include:

• Further reductions to the annual exempt amount
• Alignment of CGT rates with income tax rates
• Changes to reliefs like Business Asset Disposal Relief

Stay informed by checking HMRC’s rates and allowances page regularly.

When to Seek Professional Advice

While many straightforward share disposals can be handled without professional help, consider consulting a tax advisor if:

• You have complex share holdings or multiple disposals
• You’re unsure about qualifying for reliefs
• You have international tax considerations
• You’re dealing with employee share schemes
• Your gains are substantial (over £50,000)
• You’re planning significant financial transactions involving shares

A qualified advisor can help optimise your tax position and ensure compliance with all regulations.

Important Disclaimer: This guide provides general information only and does not constitute financial or tax advice. Capital Gains Tax rules are complex and subject to change. Always consult with a qualified tax advisor or accountant for advice specific to your situation. The calculator provides estimates based on current rules and should not be relied upon for precise tax planning.