Healthy Body Weight

Assessing Bodyweight and Health Risk

There are a number of ways that practitioners assess body weight to determine risk for chronic disease.  Assessment of weight and health risk involves using three key measures:

1. Body mass index (BMI)
2. Waist circumference
3. Risk factors for diseases and conditions associated with obesity

What is BMI?

Body Mass Index (BMI) is a person’s weight in kilograms divided by the square of height in meters. For children and teens, BMI is age- and sex-specific and is often referred to as BMI-for-age. In children, a high amount of body fat can lead to weight-related diseases and other health issues and being underweight can also put one at risk for health issues.

What is a BMI percentile and how is it interpreted?

After BMI is calculated for children and teens, it is expressed as a percentile which can be obtained from either a graph or a percentile calculator. Because weight and height change during growth and development, as does their relation to body fatness, a child’s BMI must be interpreted relative to other children of the same sex and age.

The BMI-for-age percentile growth charts are the most commonly used indicator to measure the size and growth patterns of children and teens in the United States. BMI-for-age weight status categories and the corresponding percentiles were based on expert committee recommendations and are shown in the following table:

How can I tell if my child is overweight or obese?

CDC and the American Academy of Pediatrics (AAP) recommend the use of BMI to screen for overweight and obesity in children and teens age 2 through 19 years. Although BMI is used to screen for overweight and obesity in children and teens, BMI is not a diagnostic tool. To determine whether the child has excess fat, further assessment by a trained health professional would be needed.

How is BMI used with children and teens?

For children and teens, BMI is not a diagnostic tool and is used to screen for potential weight and health-related issues. For example, a child may have a high BMI for their age and sex, but to determine if excess fat is a problem, a health care provider would need to perform further assessments. These assessments might include skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings. The American Academy of Pediatrics recommends the use of BMI to screen for overweight and obesity in children beginning at 2 years old.

This chart is an example of how sample BMI numbers would be interpreted for a 10-year-old boy:

Is BMI interpreted the same way for children and teens as it is for adults?

BMI is interpreted differently for children and teens even though it is calculated as weight ÷ height. Because there are changes in weight and height with age, as well as their relation to body fatness, BMI levels among children and teens need to be expressed relative to other children of the same sex and age.

Obesity is defined as a BMI at or above the 95th percentile for children and teens of the same age and sex. For example, a 10-year-old boy of average height (56 inches) who weighs 102 pounds would have a BMI of 22.9 kg/m. This would place the boy in the 95th percentile for BMI, and he would be considered to have obesity. This means that the child’s BMI is greater than the BMI of 95% of 10-year-old boys in the reference population.

For adults, BMI is interpreted as weight status categories that are not dependent on sex or age.

My two children have the same BMI values, but one is considered obese and the other is not. Why is that?

The interpretation of BMI varies by age and sex. So, if the children are not the same age and the same sex, the interpretation of BMI has different meanings. For children of different age and sex, the same BMI could represent different BMI percentiles and possibly different weight status categories.

See the following graphic for an example of a 10-year-old boy and a 15-year-old boy who both have a BMI-for-age of 23. (Note that two children of different ages are plotted on the same growth chart to illustrate a point. Normally the measurement for only one child is plotted on a growth chart.)