# How to Calculate your Child's Body Mass Index (BMI)

BMI, or body mass index, uses height and weight in a mathematical formula to determine a child's weight status compared to other children. BMI is not a measurement of body fat.

To calculate your child's BMI you will need to know their height and weight.

1. Take your child's weight and times it by 703.
2. Take your child's height in inches and times it by itself.

Divide the answer you got from number 1 by the answer you got from number 2.

The answer you get will be your child's BMI. It will most likely be a long decimal, round it to one decimal place.

Children and young adults between the ages of 2 and 20 with a BMI:

• Below the 5th percentile for their age are considered underweight.
• Equal to or above the 85th percentile for their age are at risk for being overweight.
• Equal to or above the 95th percentile for their age are considered overweight.

A child that has been growing continuously in the 85th-95th percentile range is probably growing normally for his or her body type. A child who has a large upward change in BMI percentile, even if not considered overweight, should be evaluated to determine the cause.

Some experts describe children at or above the 95th percentile as overweight, while other experts describe these children as obese. Similarly, children between the 85th and 94th percentiles may be described as "at risk for overweight" or "at risk for obesity."

See the BMI chart to see where your child's BMI falls.

As always, contact your child's pediatrician with any questions or concerns.

Source:

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Body mass index (BMI) for boys, ages 2 to 20

Body mass index (BMI) for girls, ages 2 to 20

Adapted from U.S. Department of Health and Human Services (2000). Clinical Data on United States Children. Available online. http://www.cdc.gov/growthcharts

Use the chart to locate your child's BMI and age.

• Children less than the 5th percentile are considered underweight.
• Children between the 5th and 85th percentiles are considered to have a normal weight.
• Children between 85th and 95th percentiles are considered at risk for being obese.
• Children in the 95th percentiles and above are considered obese (95th).
• A child who has a large upward change in BMI percentile, even if she is not considered overweight, should be evaluated to determine the cause.
• A child who has continuously been in the 85th, 90th, or 95th percentile range is probably growing normally (homeostasis) for his body type.

Primary Medical Reviewer: Caroline S. Rhoads, MD, Internal Medicine

Specialist Medical Reviewer Alan Dalkin, MD, Endocrinology

Last Updated: February 27, 2004

(603) 329-5222