Evaluating a child's BMI, or body mass index, can help to determine whether he is in a healthy weight range. Children who have higher BMIs that place them in the overweight or obese categories are at an increased risk for developing weight-related health issues, including cardiovascular disease and diabetes. BMI for children is determined using percentiles obtained after plotting BMI data on growth charts. Using BMI along with other measurement tools can help to effectively determine a child's overall weight and health status.
How to Calculate BMI for Children and Teens
Before calculating BMI, assure that you have accurate height and weight measurements for your child. For both adults and children, BMI is calculated by dividing weight in pounds by height in inches squared and multiplying by 703. There are also several online child and teen BMI calculators that can be used to obtain the BMI value.
The method of interpreting BMI values differs for children and adults. For children 2 to 20 years of age, once their BMI has been calculated, the value will be plotted on an age-and-sex specific growth chart. Gender and age specific growth charts are used because amounts of body fat differ both with age and between genders. Plotting the BMI value on a Centers for Disease Control BMI-for-age growth chart will determine a percentile for age based on the child's BMI. A child's BMI percentile demonstrates how she compares to other children of the same age and gender.
The BMI Percentiles
Four weight status categories are used to interpret the BMI-for-age percentiles determined from a growth chart. If a child has a BMI below the 5th percentile, he is considered underweight. A BMI between the 85th and 94th percentiles is considered overweight, and a BMI equal to or above the 95th percentile is considered obese. BMI percentiles that indicate overweight and obesity likely reflect the presence of excess body fat. A child with a BMI between the 5th and 85th percentiles is considered to be of a healthy weight.
Growing Along a Curve
When interpreting a child's BMI, it is important to monitor the growth trend over time rather than focusing on an individual measurement. Watching the growth pattern of a child over time allows that child's growth to be compared to other children of the same age and gender. Examining only one data plot could lead to a wrong interpretation of a child's growth. Furthermore, regularly monitoring your child's growth curve can help detect weight problems early, when they are easier to correct.
The Purpose of BMI
BMI is used as a screening tool for overweight and obesity in children and teens. Overweight children and teens are at an increased risk for being significantly overweight when they are older, as well. Identifying these problems when children are young allows for early dietary and lifestyle interventions that can prevent future weight-related health issues. The use of BMI-for-age growth charts is an important way to measure a child's growth and development. However, if you are concerned about your child's weight gain or loss, consult your pediatrician.
Problems with BMI
BMI is not a flawless measurement tool, as it does not directly measure a child's body fat. If your child has a high BMI, don't automatically assume that she is not of a healthy size. A child with a large frame or a lot of muscle can have a high BMI when in fact she does not have excess fat. This is often a problem among athletes. Also, during puberty, children may pack on extra weight, giving them a higher BMI, but this can be a normal part of development. Therefore, although BMI tends to be a reliable and cost-effective tool to evaluate a child's weight, other measurement tools such as skinfold thickness must be considered during interpretation.
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