The Body Mass Index (BMI) is a measure for expressing the ratio of weight-to-height. Health-care

The Body Mass Index (BMI) is a measure for expressing the ratio of weight-to-height. Health-care professionals use established percentile cutoff points to identify underweight and overweight in children.

Because children’s body fatness changes as they age and grow, and girls and boys differ in their body fatness as they mature, BMI for children and adolescents is gender specific, and is referred to as BMI-for-age.

Underweight: BMI-for-age, 5th percentile (to be in the 5th percentile means that compared to children of the same gender and age, 5 percent have a lower BMI).

At risk of overweight: BMI-for-age, 85th percentile to greater than the 95th percentile.

Overweight: BMI-for-age, greater than the 95th percentile.

Source: U.S. Centers for Disease Control and Prevention