What is Body mass Index?

Body Mass Index (also known as BMI) is a number calculated from a child’s weight and height. BMI is a reliable indicator of body fatness for most children and teens. BMI is not an exact measurment of body fat, but research has shown that it does correlate to direct measures of body fat. BMI can be considered an alternative for direct measures of body fat. BMI is also an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

For children and teens, BMI is age and sex specific and is often referred to as BMI-for-age.

What is a BMI percentile?

After BMI is calculated for children and teens, the BMI number is plotted on the CDC BMI-for-age growth charts (for either girls or boys) to obtain a percentile ranking. Percentiles are the most commonly used indicator to assess the size and growth patterns of individual children in the United States. The percentile indicates the relative position of the child’s BMI number among children of the same sex and age. The growth charts show the weight status categories used with children and teens (underweight, healthy weight, overweight, and obese).

BMI-for-age weight status categories and the corresponding percentiles are shown below.

Underweight - Less than the 5th percentile

Healthy weight - 5th percentile to less than the 85th percentile

Overweight - 85th to less than the 95th percentile

Obese - Equal to or greater than the 95th percentile

Source: Centers for Disease Control and Prevention