Health Calculators
Estimate the numbers people track for health and training, with the formula and its limits shown on every page.
What these calculators cover
A health number on its own tells you almost nothing. A BMI of 26 means one thing for someone who lifts and another for someone who does not, and neither reading comes from the number itself: it comes from the bands around it and from what the people who set those bands say they are for. So these pages quote the authority in its own words rather than paraphrasing it, and they say plainly where the measure stops being useful.
That matters more here than anywhere else on the site, because a health result is the kind people act on. You will find the formula in both unit systems, the exact band boundaries, and the limits the CDC and WHO put on their own measures, including the cases where they tell you to stop and see a clinician.
Which one you need
- BMI Calculator
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You want your body mass index, or the weight range that would put your height inside the healthy band.
US and metric units, the adult CDC categories, BMI Prime and the Ponderal Index, and a gauge that shows which band you land in and how close the edges are. Enter an age under 20 and it stops at the number and points you to the CDC tool built for children and teens.
Where the numbers come from
- CDC: Adult BMI Categories
- The band boundaries, quoted as the CDC writes them: healthy weight is 18.5 to less than 25, so 25.0 exactly is the next band up.
- WHO: Obesity and overweight
- The international classification and the description the WHO gives of BMI, as a surrogate marker of fatness rather than a measure of it.
- NHLBI, National Institutes of Health
- Used for the caveats: what BMI misses, and why the thresholds do not sit identically across populations.
Using these calculators well
- These are population estimates. They describe averages, not you specifically.
- Speak to a clinician before acting on any result, particularly if you have a medical condition.
- Measurements taken the same way each time are more useful than a single very precise one.