The Child BMI Calculator computes your child's Body Mass Index and BMI-for-age percentile using official CDC growth charts for ages 2-20. Enter your child's sex, age, height, and weight to instantly see if they fall into the underweight, healthy weight, overweight, or obese category.
Pick boy or girl, then toggle between imperial (ft, in, lbs) or metric (cm, kg).
Type your child's age in years and months. The CDC BMI charts cover ages 2 through 20.
Use a recent measurement for the most accurate result. Round to the nearest tenth.
See the calculated BMI, the BMI-for-age percentile, and the CDC weight category along with a plain-English interpretation.
BMI is calculated the same way for everyone: weight in kilograms divided by height in meters squared. What changes for kids is how the number is interpreted. Because children grow at different rates, the CDC plots BMI on age- and sex-specific percentile curves rather than using fixed adult cutoffs.
A BMI percentile tells you how your child compares to other kids of the same age and sex. A 60th percentile means about 60% of children that age and sex have a lower BMI.
Trends matter most. A single BMI reading is just a snapshot. What pediatricians watch for is your child's growth pattern over time - whether they are tracking along their usual curve or shifting rapidly up or down.
Data: CDC 2000 BMI-for-age growth charts. This tool provides estimates only and is not medical advice. Consult your pediatrician for diagnosis and treatment.
BMI (Body Mass Index) for children is a number that compares a child's weight to their height, age, and sex. Unlike adult BMI, child BMI is interpreted as a percentile because children's body composition changes as they grow. The CDC publishes BMI-for-age growth charts for children and teens ages 2 through 20.
Per the CDC, a BMI between the 5th and 85th percentile is considered a healthy weight for children and teens. Below the 5th percentile is classified as underweight, 85th to under the 95th percentile is overweight, and at or above the 95th percentile is obese. These categories are different from adult BMI ranges.
Children's bodies change rapidly with age, and what is normal at age 4 looks very different from age 14. For adults, BMI uses fixed cutoffs (e.g., 25 for overweight). For kids, the same BMI number can be perfectly healthy or concerning depending on age and sex, so doctors use percentiles based on CDC growth charts instead of fixed cutoffs.
A single measurement matters less than the trend over time. Talk to your pediatrician if your child's BMI percentile is below the 5th or at or above the 95th, if it shifts up or down by two or more major percentile lines between visits, or if you notice rapid weight changes. Your pediatrician can also assess factors BMI alone cannot capture, like muscle mass and growth pattern.
BMI-for-age percentile is the standard screening tool used by pediatricians and follows the official CDC LMS (Lambda-Mu-Sigma) method. It is accurate as a screening signal but it is not a direct measure of body fat. Very muscular kids may register as overweight by BMI alone, and BMI does not replace a full clinical evaluation. Use this calculator as a starting point for a conversation with your child's doctor.
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Try FamilyGPT Free →This tool provides estimates only and is not medical advice. Consult your pediatrician for diagnosis and treatment.