IntroductionObesity means having too much body fat. It is not the same as overweight, which means weighing too much. Obesity is becoming much more common in childhood. Most often, it begins between the ages of 5 and 6 and in adolescence.Child health experts recommend that children be screened for obesity at age 6. If needed, they should be referred to weight-management programs.Measuring Body FatYour child's mass index (BMI) is calculated using height and weight. A health care provider can use BMI to estimate how much body fat your child has.However, measuring body fat and diagnosing obesity in children is different than measuring these things in adults. In children:The amount of body fat changes with age. Because of this, a BMI is harder to interpret during puberty and periods of rapid growth.Girls and boys have different amounts of body fat.A BMI level that says a child is obese at one age may be normal for a child at a different age. To determine if a child is overweight or obese, experts compare BMI levels of children at the same age to each other. They use a special chart to decide whether a child's weight is healthy or not.If a child's BMI is higher than 85% (85 out of 100) of other children their age and sex, they are considered at risk for being overweight.If a child's BMI is higher than 95% (95 out of 100) of other children their age and sex, they are considered overweight or obese.Reviewed ByReview Date: 10/25/2010Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.