BMI Calculator

BMI by Age, Sex and Body Type

The BMI formula never changes. How it should be interpreted does — across sexes, life stages, athletic training, and unusual heights. This section covers who needs context beyond the standard adult categories, and what that context is.

In this section

Common questions

Does BMI change based on age or sex?
The adult BMI formula and its category thresholds are identical for men and women and for all adults regardless of age. What changes is interpretation — the same BMI can mean something different for a 25-year-old athlete than for a 75-year-old, even though the number itself is calculated the same way.
Is child BMI calculated the same way as adult BMI?
The formula is the same, but the interpretation is completely different: children and teens are assessed against age- and sex-specific growth percentiles, not the fixed adult categories, because healthy body composition changes substantially as children grow.
Why does this pillar exist separately from BMI limitations?
BMI limitations covers what the formula structurally cannot see — muscle, fat distribution, ethnicity. This section covers a different question: even accepting the formula as-is, how should the same number be read differently depending on who is being measured.