About

This site exists because most fitness calculators do not tell you where their numbers come from. You enter your height and weight, a figure appears, and there is no way to know which equation produced it, what population it was derived from, or how far off it might be for someone like you.

Every calculator here names the equation it uses, cites the paper it came from, states what that equation assumes about the person it is applied to, and says how accurate it is relative to the alternatives. Where several published equations disagree — and for body fat and basal metabolic rate they disagree substantially — the page shows the disagreement rather than hiding it behind one number.

How it is built

Static pages, no accounts, no database. The calculations run in your browser and there is no server to send them to. Every formula is checked against worked examples from its source paper in an automated test suite, which is what catches the transcription errors that quietly make a calculator wrong.

The calculations run in your browser. Nothing you type is sent anywhere, stored on a server, or logged. There is no account, no email capture and no tracking script.

What is deliberately missing

Some calculators are absent on purpose. Kidney function, body surface area for chemotherapy dosing and blood alcohol content all produce numbers that feed real decisions, and they belong with a clinician. Due date, ovulation and conception calculators are the highest-scrutiny category in health and are properly served by established medical publishers. Projecting period dates from a cycle length is arithmetic and is published here.

What these numbers are not

Every equation here was derived by fitting a curve to measurements from a specific group of people. That fit is good on average and can be poor for any given individual — an equation with a standard error of 4 percentage points is off by more than that for a substantial minority of people. Body composition equations in particular were mostly derived from small, young, mostly white samples, and they transfer imperfectly to everyone else.

None of this is medical advice, none of it is a diagnosis, and none of it replaces a conversation with a clinician who can actually measure you.