Every tool here states a formula and a source, and the whole point is that you can check them.
If a figure looks wrong, a citation is out of date, or something doesn't work with a keyboard
or a screen reader, this is where to say so.
What happens to what you send. The message goes to the site's own storage — there is
no third-party form service and no mailing list. Your IP address is not stored.
A reply address is optional, and only kept because you chose to give one. Submissions are
deleted automatically after 180 days. See the Privacy Policy.
Privacy requests
Rules of Thumb is the data controller for this site. Choose Privacy request above and say
what you need. Note that calculator inputs never leave your browser, so there is generally very
little held about anyone. Requests concerning the hosting provider's own technical logs should
also go to Cloudflare's
privacy channels, since those logs are theirs, not ours.
Before you write
Check the tool's own notes first. Most pages carry a "Field notes" and "How it works" section, and a footer stating exactly what the tool does and does not model.
Region matters. Several calculators follow one country's conventions and say so above the inputs — a US mortgage tool isn't wrong for omitting stamp duty.