UK Capital Gains Tax Calculator
Calculate your UK Capital Gains Tax on shares and securities — correctly, privately, and for free. HMRC's share matching rules (same-day, bed & breakfast, Section 104 pool) make manual calculation impractical for most portfolios. This tool handles the complexity for you.
Whether you're reporting gains on your self-assessment, planning disposals to optimise your tax-free allowance, or tracking the cost basis on RSU vests and sell-to-cover transactions — this calculator gives you an auditable breakdown of every disposal, every match, and every pool movement.
Annual Allowance Optimiser
Automatically calculate the optimal number of shares to sell to maximise usage of your Annual Exempt Amount (£3,000 for 2024/25 onwards). Choose whole or fractional shares. Make the most of your tax-free allowance before the year ends — something most calculators don't offer.
Free & Ad-Free
Completely free to use with no ads, no sign-up, and no limitations. Your tax calculation shouldn't cost you money.
HMRC Share Matching Rules
Implements the same-day rule, bed & breakfast (30-day) rule, and Section 104 pool matching in the correct priority order mandated by HMRC.
PDF Reports
Download professional PDF reports per tax year or for all years combined. Ready for your self-assessment or to share with your accountant.
Export & Re-Import
Export your trades as CSV, TXT, or Excel — store them offline and re-import next year. Your data, your control.
100% Private
Everything runs in your browser. No data is sent to any server, no cookies, no tracking. Close the tab and your data is gone.
RSU Vests & Sell-to-Cover
Enter stock vests (buy at FMV), sell-to-cover (same-day sell), and sell-all scenarios correctly for capital gains tracking.
Spouse Transfers
Supports no-gain/no-loss transfers with proper share matching. The recipient's cost basis is correctly determined via same-day and B&B rules.
Stock Splits & Foreign Currency
Handles stock splits (AMZN, GOOGL, etc.) and multi-currency trades with HMRC exchange rate lookups built in.
Multi-Year & Rate Periods
Supports tax years from 2008/09 to 2026/27 including years with multiple CGT rate periods (e.g. 2024/25 rate change).
How it works
1. Import your trades — paste from a spreadsheet, import a CSV file, or add trades manually. Each trade needs: date, buy/sell/transfer, symbol, quantity, price, fees, and exchange rate (if not GBP).
2. Review and validate — the calculator checks your trades for errors (e.g. selling more shares than you own) and highlights any issues. Edit or correct trades before calculating.
3. Calculate gains— HMRC matching rules are applied automatically: same-day first, then bed & breakfast (30-day), then Section 104 pool. You see exactly how each disposal was matched, the pool state before and after, and the gain or loss per trade.
4. Optimise & export — use the AEA optimiser to plan future sells, then download PDF reports for your tax return or accountant. Export trades for offline storage and re-import next year.
Updated annually — fully supports all UK tax years from 2008/09 through 2026/27 including the 2024/25 mid-year rate change (10%/20% to 18%/24%).
Built for UK taxpayers who hold shares, securities, ETFs, or cryptocurrency and need to calculate capital gains for their self-assessment tax return.