On this page
Where our facts come from
We rely on, in this order:
- Public health authorities: the US Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), the US National Heart, Lung, and Blood Institute (NHLBI), the UK's National Institute for Health and Care Excellence (NICE), and the National Academy of Medicine.
- Peer-reviewed studies, for formulas and findings the authorities don't cover, such as relative fat mass or adjusting BMI after an amputation.
- Official data files, such as the CDC's growth chart reference values used in our children's calculator.
Sources are listed at the bottom of each page.
How we check calculators
- Worked examples are recomputed. Every example on the site is checked by the same code the calculators use.
- Children's percentiles match CDC values. Our percentile math reproduces the CDC's published percentiles to four decimal places.
- Category boundaries are tested, including values like 24.96, which rounds to 25.0 and counts as overweight.
These checks run automatically whenever the site changes.
Pen names
Our writers use pen names. We don't present them as medical professionals, and the site doesn't claim that pages are medically reviewed. Instead, the content is built to be checked: the sources and the math are always shown.
Updates and corrections
- Pages show the date they were last updated.
- When guidelines change, we update affected pages and calculators.
- If you find an error, contact us through the About page. We correct confirmed errors promptly.
Advertising
The site is supported by ads. Advertisers have no influence on what we write, and ads never appear inside calculators or worked steps.
Not medical advice
The site is for education. It doesn't replace advice from a doctor or other healthcare professional.
Sources
Kept up to dateLast updated October 9, 2026
This page is for education and is not medical advice. Talk with a healthcare professional about your weight and health.
