About Child & Teen BMI

Body mass index (BMI) is calculated by dividing a person’s weight in kilograms by their height in meters squared. It is a simple and low-cost method to check weight categories that might cause health issues. For children and teens, BMI is adjusted for age and sex, often called BMI-for-age.

No matter the current BMI-for-age result, it’s important to help your child or teen build healthy weight habits. Regularly talk with your doctor or healthcare provider to monitor BMI-for-age. Significant weight changes in children should be reviewed and managed with guidance from a doctor or healthcare professional.

Tracking your child’s growth over time ensures they are reaching or keeping a healthy weight. A single BMI-for-age measurement isn’t enough to assess long-term weight because their height and weight will naturally change as they grow. Healthcare providers should also look at other factors like family health history, blood pressure, blood sugar, eating habits, and physical activity levels when considering BMI.

What are the health effects of childhood obesity, and how can adults help?

Childhood obesity can negatively affect the body both now and later in life. It’s important to understand the health risks linked to obesity in children.

To lower these risks, encourage kids and teens to build healthy habits, such as:

• Eating nutritious meals and staying hydrated with water.

• Making mealtimes a family activity. Involve children in cooking and let them pick healthy options.

• Finding physical activities they enjoy and being active most days of the week.

• Getting enough sleep.

• Reducing screen time.

Practicing self-care and managing stress through activities like deep breathing, meditation, yoga, or journaling.

How is BMI calculated for children and teens?

To calculate BMI using a BMI Percentile Calculator:

1. Measure the child’s height and weight.

2. Enter these values into an online calculator to find the BMI.

What is a BMI percentile, and how is it used?

When BMI is calculated for children and teens, it is expressed as a percentile. This percentile compares a child’s BMI to that of other children in the United States who participated in national surveys from 1963–1965 to 1988–1994. Since children’s height, weight, and body fat change as they grow, their BMI must be compared to others of the same age and sex.

BMI-for-age percentile growth charts are the most commonly used tool to track the size and growth patterns of children and teens in the U.S. The weight status categories and their corresponding percentiles are based on expert recommendations, as shown in the table below.

Here’s an example of how BMI numbers are interpreted for a 10-year-old boy.

How is BMI used for children and teens?

BMI is used to screen children and teens for possible weight and health issues. If a child or teen has a high BMI for their age and sex, a healthcare provider may do further tests, such as measuring skinfold thickness and reviewing family history, eating habits, and physical activity. The American Academy of Pediatrics recommends using BMI to screen for overweight and obesity starting at age 2. For children under 2 years old, the World Health Organization (WHO) standards should be used instead.

BMI-for-age should be checked at least once a year, but healthcare providers may check it more frequently. Tracking growth over time helps ensure that children and teens are reaching or keeping a healthy weight. A single BMI-for-age result cannot determine long-term weight status because children grow, and their height and weight will change.

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 the formula is the same. For kids and teens, BMI is compared to others of the same age and sex because their weight, height, and body fat change as they grow.

Obesity in children and teens is defined as having a BMI at or above the 95th percentile for their age and sex. For example, a 10-year-old boy with an average height of 56 inches and weighing 102 pounds would have a BMI of 22.9 kg/m². This would place him in the 95th percentile, meaning his BMI is higher than 95% of boys his age in the reference group. He would be classified as having obesity.

For adults, BMI is interpreted differently, using weight status categories that do not vary by sex or age.

Why aren’t healthy weight ranges provided for children and teens like for adults?

BMI between the 5th and 85th percentiles on the CDC growth charts determines a healthy weight for children and teens. Unlike adults, the interpretation of BMI for children and teens depends on their weight, height, age, and sex. For adults, BMI interpretation only depends on height and weight.

How can I know if my child is overweight or has obesity?

Overweight is defined as a BMI between the 85th and less than the 95th percentile. Obesity is defined as a BMI at or above the 95th percentile for children and teens of the same age and sex.

Can I use an adult BMI calculator to check if my child has obesity?

The adult BMI calculator is only for individuals 20 years and older. It provides a BMI value but not a BMI percentile. Since BMI percentiles are necessary for assessing children and teens, the adult calculator is not suitable for this purpose.

Why would two children with the same BMI value be classified differently?

The meaning of BMI varies based on age and sex. If the children are not the same age or sex, their BMI will be interpreted differently. For example, a 10-year-old boy and a 15-year-old boy with the same BMI value may fall into different BMI-for-age categories.

Does a high BMI in an athlete mean they are overweight?

Athletes may have a higher BMI due to increased muscle mass rather than higher body fat. A trained healthcare provider can assess overall health and risks more accurately. BMI is just a screening tool and doesn’t account for factors like fat distribution, genetics, diet, or fitness level, all of which influence disease risk.