About 123BMICalculator

123BMICalculator is a free set of 16 calculators for body mass index and the measures that go with it: BMI for adults, children and teens, older adults and Asian cut-offs; healthy, ideal and goal weight; pregnancy weight gain; body fat, waist-to-height and waist-to-hip ratios and body roundness; and the calories you burn. There are no accounts, no ads and no tracking.

What we care about

  • The right method, not a rough one. Adult BMI is rounded and classified exactly as the CDC does it, so our healthy ranges match the CDC's own figures. Children's percentiles come from the CDC's reference data, including the 2022 extended charts above the 95th percentile, and reproduce the CDC's published check values.
  • Showing the working. Every calculator has a worked example with real numbers, the formula it uses, its limits, and the sources behind it — the WHO, the CDC, NICE, the American Academy of Pediatrics, the Institute of Medicine and the original research papers.
  • Honest about BMI. BMI is a useful screen and a poor diagnosis. Each page says where it falls short, and the waist and body-fat calculators are there to fill the gap.
  • Fast and private. Pages load in a moment, work without JavaScript, and nothing you enter is stored. See the privacy policy.
  • Easy to share. Every result has its own link and its own picture — if you choose to share it.

How the calculators are checked

Each calculator runs the same code whether you see the result on the page, as you type, or in a shared picture, so the three can never disagree. The worked examples on every page are calculated live, and an automated test suite checks the arithmetic before every release — including CDC's healthy-weight ranges by height and the CDC growth-chart reference values.

Reviewed and updated

The content is reviewed against the latest guidance, most recently the 2025 Lancet Diabetes & Endocrinology commission on the definition of clinical obesity and NICE's 2025 guideline on overweight and obesity.

Part of the 123 family

123BMICalculator is made by the team behind 123Calculator.app (hundreds of free calculators) and 123AgeCalculator.com (exact age calculators): simple, free web tools that do one job well.

Contact

Found a mistake, or want a calculator we don't have? Email hello@123bmicalculator.com — corrections are fixed quickly.