Why BMI is flawed (and still useful)

BMI gets a lot of criticism, and most of it is fair. It is also still useful when you understand its limits. Both things are true.

What BMI gets wrong

• It cannot tell muscle from fat. BMI only sees total weight, so a muscular person and a person carrying extra fat can share the same number.
• It ignores where you carry fat. Fat around the organs is more harmful than fat on the hips, but BMI treats all weight the same.
• It does not adjust for age or sex. Body composition shifts with both, yet the adult categories are identical for everyone.

In 2023 the American Medical Association acknowledged these gaps and called BMI alone an imperfect clinical measure.

Why it has not gone away

BMI survives because it is cheap and fast. It needs two numbers anyone can get, and across large groups it tracks health risk well enough to be a useful first screen. The problem is only when people treat it as the final word on one person.

Use it the right way

Calculate your BMI, then add the context it misses: your body fat percentage and your FFMI. The BMI calculator shows all of these together, so you get the screen and the fuller picture in one place.