How to Calculate a Child's Median BMI

Body mass index (BMI) is an estimation of body fat mass based on an individual's height and weight. The formula for calculating BMI is the same for both children and adults. However, because the established range for healthy body fat percentage varies with age among children and teens and differs according to gender, the standards used to interpret the meaning of BMI figures is different for persons under 20 than it is for adults. Too account for this variability, growth charts are used to indicate BMI percentile ranking. Percentile ranking is what signifies the relative weight status of a child.

Things You'll Need

• Weight scale
• Measuring tape

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Instructions

Using CDC Online Calculator to Assess BMI

• 1

  Weigh your child or use your child's last known weight from his most recent doctor's visit. Measure your child's height, or you may again use your child's last known weight from his most recent doctor's visit.

• 2

  Use the CDC: BMI Calculator resource located at the end of this article.

• 3

  Enter the child's birth date and the date of his last weighing, select your child's gender, and enter his height and weight. Click "Calculate."

• 4

  Interpret the results of the BMI calculation. Underweight children will fall under the 5th percentile for their gender and age group. Children of a healthy weight will fall within the 5th and 84th percentile for their gender and age group. Overweight children will fall within the range the 85th to 94th percentile for their gender and age group. Obese children will be equal to or above the 95th percentile for their gender and age group.

Using the CDC Growth Chart to Assess BMI

• 5

  Use the CDC Graphic Growth Chart resource located at the end of this article. Choose the chart appropriate for your child's gender.

• 6

  Print this chart. Using a pencil, mark the graphic coordinates where your child's age and weight intercept.

• 7

  Determine which sloping lines your coordinates lie within. This will tell you the percentile range for your child. Underweight children will fall under the 5th percentile for their gender and age group. Children of a healthy weight will fall within the 5th and 84th percentile for their gender and age group. Overweight children will fall within the range the 85th to 94th percentile for their gender and age group. Obese children will be equal to or above the 95th percentile for their gender and age group.