BMI percentiles show how kids' measurements compare with others the same gender and age. For example, if a child has a BMI in the 60th percentile, 60% of the kids of the same gender and age who were measured had a lower BMI.
BMI is not perfect. For example, it's very common for kids to gain weight quickly — and see the BMI go up — during puberty. Your doctor can help you figure out whether this weight gain is a normal part of development or whether it's something to be concerned about.
Kids can also have a high BMI if they have a large frame or a lot of muscle, not excess fat. And a kid with a small frame may have a normal BMI but too much body fat.
Although BMI is not a direct or perfect measure of body fat, kids at or above the 95th percentile are considered obese, a term doctors use to indicate excess body fat, which increases the risk of weight-related health problems.
Kids who measure at the 85th to 94th percentiles are considered overweight, because of excess body fat or high lean body mass. A child whose BMI is between the 5th percentile to 85th percentile is in the healthy weight range. A child with a BMI below the 5th percentile is considered underweight.
Also, it's important to look at the BMI numbers as a trend instead of focusing on individual numbers. Any one measurement, taken out of context, can give you the wrong impression of your child's growth.
The real value of BMI measurements lies in viewing them as a pattern over time. That allows both doctor and parents to watch a child's growth and determine whether it's normal compared with that of other kids the same age.
While BMI is an important indicator of healthy growth and development, if you think your child may be gaining or losing weight too fast, talk to your doctor.
Reviewed by: Mary L. Gavin, MD
Date reviewed: March 2011