How it works
Four steps
Upload your statements and the HMRC matching rules are applied to produce your 2025/26 figures.
Add your CSVs
Download your transaction history and drop the files in. We detect the broker automatically.
Enter your income
Enter your total taxable income for 2025/26.
The rules get applied
Same-day trades first, then anything bought back within 30 days, then the Section 104 pool. In that order, every time.
Get your numbers
The figures for each SA108 box, every disposal, and a PDF to keep.
The three matching rules, in order
Same-day rule
Shares you sell are first matched against any of the same shares you bought on the same day.
30-day rule
Next, sales are matched against shares you buy back within the following 30 days. This is the 'bed and breakfast' rule that stops people selling and instantly rebuying to bank a loss.
Section 104 pool
Anything left is matched against your Section 104 pool: the running total quantity and average cost of everything you still hold. HMRC reference CG51560.
Cryptoassets are not included
This calculator covers shares, funds and ETFs. It does not calculate Capital Gains Tax on cryptoassets. HMRC treats cryptoassets as property, with a separate Section 104 pool for each token.