We build free, accurate health calculators for real people — no jargon, no sign-ups, no hidden costs. Just clear answers about your body, whenever you need them.
KnowYourBody.Online was built out of a simple frustration: too many health websites are buried in caveats, and require you to create an account just to find out how much water you should drink.
We set out to build something better — a clean, fast, no-nonsense collection of health calculators that work the way people actually think. Imperial measurements by default for UK users. Results in plain English. No email required. No data sent anywhere.
We’re a small independent project, not a healthcare company. Our goal is simply to give people easy access to the kind of back-of-the-envelope health estimates that used to require a trip to the GP — or a degree in maths.
Everything we build is guided by four principles that we take seriously.
Every calculator on this site is hand-coded from scratch — no templates, no third-party widgets. Each one is designed to be fast, accurate, and genuinely useful on a phone as much as a desktop.
We use established, widely-referenced equations for all our calculators. Here is a quick summary of what powers each one, and where the formulas come from.
All formulas produce population-level estimates. Individual results will vary. Please read our disclaimer for a full explanation of each calculator’s limitations.