What this tool is
The calculator applies the HMRC share matching and pooling rules within its stated scope to the transaction data you provide, to show the capital gains and losses calculated in accordance with those rules. It is provided for information only, and should not be relied upon as a substitute for professional advice.
Not tax, financial or legal advice
This tool does not provide tax, financial or legal advice, and using it does not create any advisory relationship. It is not a substitute for professional advice from a qualified accountant or tax adviser. You are responsible for checking the results before relying on them, including when completing a Self Assessment return, and for seeking professional advice on your own circumstances. See the scope page for the specific simplifications and known limitations in the calculation logic.
No warranty
The calculator is provided "as is", without warranty of any kind, express or implied, including any warranty as to its accuracy, completeness, or fitness for a particular purpose. Tax legislation and HMRC guidance can change, and this tool may not reflect every such change at all times.
Limitation of liability
We are not responsible for losses arising from your use of, or reliance on, the calculator or its results where the loss is caused by your failure to check the results or by circumstances outside our reasonable control. This includes any penalty, interest or additional tax liability resulting from your reliance on an incorrect or incomplete calculation.
Nothing in these terms excludes or limits any liability that cannot lawfully be excluded or limited, or affects your statutory rights.
Your data
See the Privacy Policy for how your transaction data is handled. In short, your transaction data is processed in memory only and its contents are not retained as transaction records. We retain limited, aggregated usage statistics about how the calculator is used and not transaction data.
We use optional Google Analytics cookies to see how the site is used. See our Privacy Policy and Cookie Settings.
Acceptable use
You may use GainsEngine for your personal or explicitly licensed commercial capital gains calculations. However, you must not use automated tools, such as scrapers or bots or API clients, to extract data, examples, or calculation results from the website. You are also strictly prohibited from reverse-engineering the calculation logic or using the site's inputs and outputs to train, validate, or build any other software, including artificial intelligence models. We reserve the right to block access to protect the service from automated abuse.
Changes to these terms
These terms may be updated from time to time. Continued use of the calculator after a change constitutes acceptance of the updated terms.
Contact
Questions about these terms can be sent via our feedback form.
Last updated: 29 September 2026.