Editorial Policy
TheFitnessCalculator.com publishes five calculators and a set of guides explaining what each one measures. This page sets out where the numbers come from, who writes the guides, and what the tools are not suitable for.
Who writes this site
The guides are written and maintained by the site’s editorial team rather than a single named author. Nobody on the team is a physician or a registered dietitian, and the site does not present itself as a clinical resource. What the team does is read the primary literature behind each equation and report it accurately, including the error bars that calculator sites usually leave out.
Where a guide makes a factual claim about an equation’s origin or accuracy, it links to the study it came from. Those links go to PubMed, the National Academies, the World Health Organization or the journal itself, so you can check the claim without taking our word for it.
Which equations the calculators use
- BMI. Weight in kilograms divided by height in metres squared, with the World Health Organization category thresholds at 18.5, 25 and 30.
- Calories and TDEE. The Mifflin–St Jeor equation (1990) for basal metabolic rate, multiplied by a physical activity level between 1.2 and 1.9. Mifflin–St Jeor was chosen because a 2005 systematic review found it the most accurate of the common equations for non-obese adults.
- Body fat. The US Navy circumference method developed at the Naval Health Research Center, using neck, waist, height and, for women, hip.
- Ideal weight. The Devine (1974) and Robinson (1983) formulas, shown alongside the healthy BMI weight range, because neither formula was built as a body composition target.
- Water intake. A 35 ml per kilogram of body weight baseline plus an allowance for exercise, referenced against the Institute of Medicine adequate intake levels.
How accurate any of this is
Every equation on this site is a population-level estimate applied to one person, and each one carries a stated error range in its guide. Mifflin–St Jeor lands within 10% of measured metabolic rate for roughly four adults in five, which still means a 178 calorie spread on a 1780 calorie result. The Navy tape method carries a standard error of 3 to 4 percentage points.
BMI cannot distinguish muscle from fat at all.
None of that makes the numbers useless. It makes them starting points that you correct with your own data over two to four weeks. The guides say so repeatedly, and the calculators print ranges rather than single figures wherever a range is the more honest answer.
Corrections and updates
Guides carry a published date, and an updated date whenever the text changes materially. If you find an error, a broken calculation or a citation that does not support the claim attached to it, tell us through the contact page and we will correct it.
What this site is not
These are educational tools for healthy adults. They are not medical advice and they do not replace a doctor or a registered dietitian. If you are pregnant or breastfeeding, under 18, over 65, managing a medical condition, taking medication that affects fluid balance or metabolism, or recovering from an eating disorder, treat every output here as background reading and take your actual guidance from a clinician. The full terms are in the medical disclaimer.
How the site makes money
The calculators are free and require no account. The site carries advertising, and ad revenue has no influence on what the guides say. There are no affiliate links to supplements, programmes or equipment anywhere on the site.