Health & Body Calculators

Every tool in this category is a named published formula, and the name and the constants travel with the result. Body mass index is the WHO definition, weight in kilograms divided by height in metres squared. Basal metabolic rate uses the Mifflin-St Jeor equation, with its +5 and −161 constants printed in the formula line. Body fat uses the US Navy circumference method with its logarithmic coefficients, ideal weight shows the Devine, Hamwi, Robinson and Miller formulas side by side, lean body mass shows Boer, James and Hume together, body surface area pairs Mosteller from 1987 with Du Bois and Du Bois from 1916, heart-rate zones are built by the Karvonen method from a Fox or Tanaka maximum, the due-date calculator counts by Naegele's rule, and activity expenditure takes its MET values from the published Compendium of Physical Activities. A figure whose formula is named can be checked, reproduced and compared; a figure from an unnamed model can only be trusted, and this category does not ask for trust it has not earned.

The category follows one rule without exception: these tools compute an index or an estimate and nothing more. They do not interpret a person, they do not diagnose, and they do not advise. Where published reference bands exist they are printed as tables for the reader to locate a number against them directly — the WHO BMI bands, from below 18.5 through 30 and above, and the Karvonen zone table, from 50–60% of heart-rate reserve up to 90–100% — stated as published facts, in the publisher's own groupings. Where formulas disagree, as the three lean-body-mass equations do by several kilograms on identical inputs, the disagreement is shown rather than resolved by quietly picking one. A due date is a count of 280 days from a stated starting point, a water figure is the output of a stated rule of thumb that varies with climate, diet and individual factors, and a calorie figure is a population equation applied to the numbers entered. The arithmetic is the whole product; what any of it means for a particular person is a question for a clinician who knows that person.

The privacy rule that applies across Kwikfig applies with extra force here. Body measurements and pregnancy dates are among the most personal numbers a person ever types into a website — weight, circumferences, resting heart rate, the first day of a last period. Every calculator in this category runs entirely in the browser, on the device in front of the reader. Nothing entered is uploaded, stored, tracked or shared, there is no account and no history, and closing the tab removes the figures completely. That is not a policy promise bolted onto a server process; it is the architecture. The page that calculates a BMI never transmits the weight and height it calculated from, and a reader can verify the claim by loading a tool, disconnecting from the network, and watching it work identically offline.