Contact
Questions, corrections and bug reports are all welcome. Mail goes to the person who maintains the calculator, not to a support desk — so replies are not instant, but they are replies from someone who can actually change the tool.
Reporting a wrong figure
If a calculation looks wrong, the most useful message says what you entered, what the calculator produced, and what you expected instead — plus the tax year. A few sample trades that reproduce it are better still.
Please send made-up figures, not your real ones. Nothing you type into the calculator ever leaves your browser (see privacy), and an email is not the place to start sending real trade data. A handful of invented trades with the same shape reproduces a bug just as well.
Issues in the calculation engine
The matching rules, rates and tax-year data live in a separate open-source library, capital-gains-calculator. If the bug is in the arithmetic rather than the website, raising it there gets it to the code directly — bug reports, feature requests and contributions are all welcome. (The library is open source; the website around it is not.)
github.com/damiantanase/capital-gains-calculatorAnswered already, most likely
Before writing: the FAQ covers the questions that come up most, the manual documents every field and import format, methodology explains how the figures are produced and checked, and about says who publishes this and on what basis.
Disclaimer: This calculator does not provide tax advice, and no reply sent from this address is tax advice either. For guidance on your own position, consult a qualified accountant or tax adviser.