What is body mass index (BMI)?

Body mass index (BMI) is a measure of weight adjusted for height, calculated as weight in kilograms divided by the square of height in meters (kg/m2).

Because the BMI calculation relies solely on height and weight it is easily accessible to measure, it has become a widespread and longstanding index.

BMI is used as a measure to track weight status in populations and as a screening tool to identify potential weight problems in individuals. Because BMI does not diagnose the body fatness or health of an individual, further assessment using more comprehensive metrics is needed to diagnose true health risks.

Limitations of BMI

BMI has many limitations. It is a poor tracking tool for weight change because there is no way to identify if changes in your weight are in fat or muscle.

Because BMI does not distinguish fat mass from lean mass, it may overestimate body fat in athletes and others who have a muscular build. It may also underestimate body fat in older persons and others who have lost muscle.

Also, for adults, there are no racial, gender, or age-specific reference ranges for BMI making it less useful across different population groups.