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.
Key Features
Annual Allowance Optimiser
Only hereCalculate exactly how many shares to sell to use your full £3,000 tax-free allowance. Plan disposals across tax years to minimise your CGT bill.
Private by Design & Open Source
Privacy firstYour trades are calculated right in your browser and never leave your device. No tracking, no ads, no sign-up. The calculation engine is fully open source for complete transparency.
Free, No Ads, No Sign-Up
Always freeCompletely free with no ads, no account required, and no limitations. Your tax calculation shouldn't cost you money.
HMRC Share Matching Rules
Same-day, bed & breakfast (30-day), and Section 104 pool rules in correct HMRC priority order. See exactly how each disposal is matched with full pool traceability.
Spouse & Civil Partner Transfers
Transfer shares between partners to double your tax-free allowance. Implements HMRC's no-gain/no-loss rules (TCGA 1992 s58).
RSU Vests & Corporate Actions
Handles vesting events, sell-to-cover, sell-all, and stock splits with correct cost basis adjustments. Built for tech workers with equity compensation.
Multi-Currency
Supports GBP, USD, and EUR trades. Automatically fetches official HMRC monthly exchange rates for accurate conversion.
Multi-Year Support
All tax years from 2008/09 to 2026/27 with per-year summaries. Handles mid-year rate changes like the 2024/25 shift from 10%/20% to 18%/24%.
Reports & Export
PDF reports for your self-assessment, interactive charts for analysis, CSV/Excel export for offline storage. Re-import next year.
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.