Sources & Methodology

How a formula gets chosen

A calculator earns its place here if its formula is published and traceable to a named public source — a government health body, a national health service, or a documented dataset. That source is linked on the calculator's own page, so you can check the claim rather than trust us.

Where two formulas disagree, the one traceable to a named authority is used. Where a formula is genuinely contested, the calculator says so on its page instead of quietly picking a winner.

How sources are cited

Citations name the organisation and the document, and link to the publisher's own page. We do not cite a source we have not read, and we do not cite an aggregator that restates a study we could have read directly.

Every calculator cites its source in plain text as well as in a link, so the attribution survives being copied or summarised elsewhere.

The formulas in use

BMI uses the standard weight-over-height-squared formula, with categories from the CDC adult ranges. It is a population screening measure: it does not distinguish muscle from fat, and it is not designed for children or pregnancy.

Basal metabolic rate uses the Mifflin–St Jeor equation, which requires sex as an input because the formula itself is sex-specific. Resting energy expenditure is shown instead of a daily total — see below for why.

Body fat percentage uses the Deurenberg body mass index formula, which needs a body mass index first. It is an estimate from height, weight and age, not a measurement, and it is least reliable at the extremes of body mass index.

Heart rate zones use percentage of maximum heart rate, where maximum is estimated by a standard age-based formula. That estimate has a wide margin of error in individuals, so treat the zones as a guide to intensity rather than a precise boundary.

Water intake is a general population recommendation scaled to body mass, adjusted for activity and climate. It is not a requirement for one person and it does not account for fluid from food or other drinks.

Running pace converts distance and time to a sustainable pace, and back to predicted finish times at that pace. Race prediction from a single split is an extrapolation, not a forecast.

Daily calories and the meal calculator use the USDA FoodData Central dataset. Energy values are laboratory analyses of sampled foods, so a real carrot will not match the database exactly.

What is deliberately missing

There is no TDEE calculator here. Daily energy expenditure requires an activity multiplier applied to a resting figure, and the multipliers in circulation are estimates of estimates — they inherit the error of the resting equation and add more on top.

Presenting a confident single number for it, next to a BMR calculator that looks equally precise, would imply a reliability that the underlying research does not support. We would rather publish the resting figure and say plainly that the daily total is not established. The BMR calculator explains this where you will actually see it.

Estimates, ranges, and diagnoses

A calculator on this site shows an estimate: the output of a formula given your inputs. A reference range is the band a healthy population falls into. A diagnosis is a clinical judgement made by a clinician who can examine you.

HealthCalc produces the first and cites the second. It does not produce the third, and no page here should be read as if it did.

Verification

Every published figure on this site can be checked against the source linked beside it. If a formula and a cited source disagree, the source is right and the calculator is a bug — please tell us.