Health calculators that show their working

Every tool on this site prints the formula it used, the publication that formula came from, and worked examples computed by the same code running in your browser.

• Acute:Chronic Workload Ratio Calculator

  An acute:chronic workload ratio calculator turns the weekly training totals you already record into the ratio used in the sports-medicine literature, and reports the ranges those papers actually named instead of inventing categories in between.

• BMI Calculator

  Body mass index is weight divided by height squared.

• Body Fat From BMI Calculator

  This page calculates body fat percentage from the four numbers most people already know - height, weight, age and sex - using the prediction formula published by Deurenberg and colleagues in 1991.

• Caffeine Half-Life Calculator

  Enter how much caffeine you took and how long ago, and this page tells you how many milligrams are still in your body.

• Calorie Calculator

  Most calorie calculators on the internet multiply a resting equation by an activity factor.

• Heart Rate Recovery Calculator

  Heart rate recovery is one subtraction: the heart rate you were at when you stopped, minus the heart rate sixty seconds later.

• Heart Rate Zone Calculator

  A heart rate zone calculator has to pick a maximum heart rate first, and the published equations disagree by more than ten beats per minute for the same person.

• Resting Energy Expenditure Calculator

  Resting energy expenditure (REE) is the kilocalories a body burns at rest, and the equation behind most "calorie calculator" pages on the internet produces it from four numbers: weight, height, age and sex.

• US Navy Body Fat Calculator

  The US Navy body fat method estimates body fat from a tape measure - neck, waist and, for women, hip circumference - with no weigh-in, no scan and no skinfold calliper.

• VO2 Max From Heart Rate Calculator

  This page estimates VO2max from the ratio between your maximum and resting heart rate, using the proportionality factor published by Uth and colleagues.

• Waist to Height Ratio Calculator

  Waist-to-height ratio (WHtR) is one number divided by another: your waist circumference by your height.

• Water Intake Calculator

  Public health guidance often expresses total water intake as an amount per kilogram of body weight.

What you can check on any page here

Each tool page states its formula in plain arithmetic, names the publication the formula or the reference constants came from, and prints worked examples that were computed by the same function your browser runs, at the moment the page was built. If a number on a page looks wrong, that makes it possible to find out where: the formula, the reference data, or your own inputs. Nothing on this site asks you to take a figure on trust.

Where a source gives a range rather than a single value, the pages show the range and carry it through the calculation, because a midpoint presented alone reads as more precise than the evidence behind it. Reference data that could not be traced to a primary publication does not appear at all; it is left out rather than estimated.

Tools whose source citations have not been checked against the original publication are marked noindex and stay out of this list and out of the sitemap.