UK Capital Gains Tax.
Calculated.
Upload your trades, apply HMRC share matching rules, and generate your SA108 report — free, instant, and private.
| whatsmycgt | Accountant | Manual / spreadsheet | |
|---|---|---|---|
| Cost | Free | £200–500+ | Free |
| HMRC share matching | ✓ Automatic | ✓ | Manual & error-prone |
| SA108 box figures | ✓ Instant | ✓ | ✗ |
| Full audit trail | ✓ Every disposal | Varies | ✗ |
| Turnaround time | Seconds | Days–weeks | Hours–days |
| Data privacy | ✓ Never leaves device | Shared with firm | ✓ Local |
| Multi-year support | ✓ | Per engagement | Complex |
- Date — trade date in DD/MM/YYYY or any Excel date format
- Ticker / Symbol — the stock or fund identifier (e.g. VWRL, AAPL)
- Type / Action — must contain
BuyorSell - Quantity / Shares — number of shares traded
- Price — price per share converted to GBP
- Brokerage / Fees — broker commission for the trade converted to GBP (can be 0)
| Date | Ticker | Type | Quantity | Price | Brokerage |
|---|---|---|---|---|---|
| 01/03/2024 | VWRL | Buy | 100 | 82.50 | 5.00 |
| 15/09/2024 | VWRL | Sell | 50 | 91.20 | 5.00 |
Drop your spreadsheet here
or click to browse · .xlsx / .xls / .csv / .ods
0 Data Warnings Found
- Tax Year — UK tax years run 6 April to 5 April. Select a specific year or "All years" to see every tax year in your data. SA108 values are generated per year.
- CGT Rate — depends on your total taxable income. Basic rate taxpayers pay a lower CGT rate; higher and additional rate taxpayers pay more. Check HMRC's current rates and enter yours as a whole number. The default reflects the current standard basic rate.
- Annual Exemption — the tax-free allowance set by HMRC each year. The default is updated automatically based on the selected tax year. Check HMRC for the latest threshold if you're unsure.
- Unrealised gains — optionally enter current market prices for positions you still hold to see paper gains/losses. This doesn't affect your tax calculation.
Your CGT Report
Frequently Asked Questions
How does this UK capital gains tax calculator work?
Upload your share trade history as a CSV or Excel file containing your buy and sell transactions. The calculator applies HMRC's three share matching rules — the same-day rule, the 30-day bed and breakfast rule, and Section 104 pool averaging — to each disposal. It calculates your taxable gains and allowable losses for each tax year and generates SA108 box figures ready for your self-assessment tax return.
What are the HMRC share matching rules for CGT?
When you sell shares, HMRC requires disposals to be matched against acquisitions in a strict order. First, shares are matched against any bought on the same day (same-day rule). Then against shares bought within the next 30 days (bed and breakfast rule). Finally, remaining shares are matched against your Section 104 pool — a running weighted average cost of all your holdings in that stock.
Is this calculator really free?
Yes. whatsmycgt is completely free with no subscriptions, sign-ups, or hidden charges. All calculations happen in your web browser — your financial data never leaves your device and is discarded when you close the page.
How does the bed and breakfast rule work?
The bed and breakfast rule (also called the 30-day rule) prevents you from selling shares and rebuying them shortly after to create an artificial loss. If you sell shares and repurchase the same shares within 30 days, HMRC matches the sale against the repurchase rather than your original cost basis. This means the gain or loss is based on the new purchase price, not your historic holding. This calculator automatically detects and applies the bed and breakfast rule to all your disposals.
Can I use this with Trading 212, Freetrade, or IBKR exports?
Yes. The calculator accepts any CSV or Excel file with columns for date, ticker/symbol, buy or sell type, quantity, price per share, and brokerage fees. Most broker exports from Trading 212, Freetrade, Hargreaves Lansdown, Interactive Brokers (IBKR), and other UK platforms work with minimal adjustment. All amounts must be converted to GBP before uploading.
What is a Section 104 pool?
A Section 104 pool (or holding) is HMRC's method of averaging the cost of shares in the same company. Each purchase increases the pool's total cost and quantity. When you sell shares that aren't matched by the same-day or bed and breakfast rules, they're matched against the pool at its weighted average cost per share. This calculator tracks every pool automatically.
How do I report capital gains on my self-assessment tax return?
Capital gains from shares are reported on the SA108 supplementary page of your self-assessment tax return. This calculator maps your gains directly to SA108 boxes — including total disposals, gains, losses, and the annual exempt amount — so you can transfer the figures straight to your tax return or HMRC's online filing system.
Is my data safe and private?
Yes. All processing happens entirely within your browser using client-side JavaScript. No trade data, calculations, or personal information is ever transmitted to any server. There are no user accounts, no databases, and no tracking of your financial data. When you close or refresh the page, everything is permanently discarded.