Your child's BMI percentile indicates where they fall relative to other children of the same age and sex based on CDC growth chart reference data. A percentile below the 5th indicates underweight, which may warrant evaluation for nutritional deficiency, chronic illness, or eating disorders. The 5th to 84th percentile range is considered healthy weight. The 85th to 94th percentile is classified as overweight, and the 95th percentile or above is classified as obese. Severe obesity is defined as BMI at or above 120% of the 95th percentile.

A single BMI percentile measurement provides a snapshot, but tracking the trend over time is far more valuable. A child who has consistently tracked along the 80th percentile is quite different from one who has rapidly crossed from the 50th to the 90th percentile over six months. Discuss the trend, not just the number, with your pediatrician.

Use this calculator during routine well-child visits for children and adolescents aged 2 to 20 years. The CDC recommends annual BMI screening for all children in this age range. It is particularly important when there are concerns about a child's growth trajectory, when evaluating for obesity-related comorbidities (insulin resistance, dyslipidemia, hypertension), or when a child has risk factors such as family history of obesity or type 2 diabetes.

For children under age 2, weight-for-length percentiles should be used instead of BMI-for-age. For adults over 20, standard adult BMI categories apply without the need for age- and sex-specific percentiles.

BMI percentile is a screening tool, not a diagnostic measure. It does not distinguish between fat mass and lean mass — a muscular adolescent athlete may have a high BMI percentile without excess body fat. Conversely, a child with low muscle mass may have a normal percentile despite elevated body fat percentage.

The CDC growth charts were derived primarily from U.S. population data and may not perfectly reflect healthy growth patterns for all ethnic groups. The WHO growth standards (used for children under 2 and in many countries outside the U.S.) use a different reference population. Additionally, BMI percentile does not capture fat distribution, which is increasingly recognized as important for metabolic risk even in children.