Pediatric BMI Calculator
Calculates BMI for children and teens aged 2–19 using weight and height. Use it during well-child visits or growth monitoring to screen for underweight, healthy weight, overweight, or obesity.
About this calculator
Body Mass Index (BMI) is a screening tool that relates body weight to height. For children, the formula is identical to the adult version: BMI = weight (kg) / (height (m))². Since height is entered in centimeters, the formula converts it first: BMI = weight / (height / 100)². Unlike adults, a child's BMI result is not interpreted against fixed thresholds. Instead, it is plotted on age- and sex-specific CDC or WHO growth charts to determine a BMI-for-age percentile. A result below the 5th percentile indicates underweight, 5th–84th is healthy weight, 85th–94th is overweight, and 95th percentile or above is considered obese. Always consult a pediatrician for clinical interpretation.
How to use
Suppose a 10-year-old child weighs 35 kg and stands 140 cm tall. Step 1 — Convert height to meters: 140 / 100 = 1.40 m. Step 2 — Square the height: 1.40² = 1.96. Step 3 — Divide weight by that value: 35 / 1.96 = 17.86. The child's BMI is approximately 17.9 kg/m². Step 4 — Plot this value on a CDC BMI-for-age chart for the child's sex to find the percentile and interpret whether the weight status is healthy.
Frequently asked questions
How is pediatric BMI interpreted differently from adult BMI?
Adult BMI uses fixed cut-off values (e.g., 18.5–24.9 for healthy weight), but these thresholds do not apply to children because body fatness changes naturally with age and differs between boys and girls. Pediatric BMI is expressed as a percentile relative to other children of the same age and sex using standardized growth charts. This percentile-based approach accounts for normal growth patterns throughout childhood and adolescence. A healthcare provider uses these charts alongside other clinical information to assess a child's weight status.
What is a healthy BMI percentile range for children and adolescents?
According to the CDC, a BMI-for-age percentile between the 5th and 84th percentile is considered a healthy weight for children and teens. Below the 5th percentile is classified as underweight, the 85th to 94th percentile is overweight, and the 95th percentile or above is classified as obese. These categories are screening tools, not diagnoses, and a single measurement should be interpreted cautiously. Trends over multiple visits and other health indicators give a fuller picture of a child's nutritional status.
How often should a child's BMI be calculated to monitor healthy growth?
Most pediatric guidelines recommend calculating BMI at every routine well-child visit, which typically occurs annually for school-age children and adolescents. For younger children, visits are more frequent — at 2, 4, 6, 9, 12, 15, 18, and 24 months — allowing close monitoring during rapid growth phases. Tracking BMI over time is more informative than a single snapshot because it reveals growth trends. If a child's percentile is rising sharply or falling, a clinician may recommend dietary or lifestyle evaluation.