BMI Calculator

What is BMI?

Body Mass Index (BMI) is a simple formula — weight divided by height squared — that was originally developed in the 1830s by Belgian mathematician Adolphe Quetelet to study population averages, not to assess individual health. Today it's used as a rough, low-cost screening measure, but it has real limitations.

What BMI Doesn't Measure

• It doesn't distinguish muscle from fat — athletes with high muscle mass often show as "overweight" despite low body fat.
• It doesn't account for age, sex, or bone density.
• It is not designed for children or teenagers. Under age 20, doctors use BMI-for-age growth charts and percentiles instead of the adult categories shown below — a single BMI number means something different for a growing teenager than for an adult.
• It says nothing about diet quality, fitness level, or overall health on its own.

For these reasons, BMI is best treated as one small data point — not a diagnosis, and not something to base decisions about eating or exercise on by yourself.

Try the Calculator

For educational use. If you're under 20, talk to a parent/guardian or doctor about what a healthy range looks like for your age — the categories below apply to adults only.

Sources

• CDC — About Body Mass Index
• World Health Organization — Obesity and Overweight

Reviewed by the Polaris Youth editorial team. Last reviewed: July 2026.