BMI is a screening tool, not a diagnosis

Body mass index is a calculation based on height and weight. For adults, it is commonly used as one screening measure of weight relative to height. It cannot, by itself, describe a person’s health or body composition.

Reviewed: September 2026 · General education, not medical advice

What the calculation does well

BMI is quick, inexpensive, and consistent. For adults 20 and older, standard categories provide a common way to identify when it may be useful to look more closely at health risks. CDC describes BMI as a screening measure: one piece of context, not a conclusion.

What it leaves out

BMI does not directly measure body fat, muscle mass, blood pressure, blood sugar, cholesterol, fitness, diet, sleep, medications, or family history. People with the same BMI can have very different health profiles. Children and teens use age- and sex-specific growth charts rather than adult categories.

Get a fuller picture

Where appropriate, a clinician may consider BMI alongside medical history, examination findings, laboratory results, health behaviors, and personal goals. A consistently measured trend can be more useful than reacting to a one-time reading, but it still needs context.