Child BMI Calculator (& Teen)

Sex

Age

Weight

Height

Based on approximated CDC BMI-for-age growth charts, the reference used for children and teens ages 2–20 (younger children use separate WHO growth standards — see our Baby & Toddler BMI Calculator). This is an estimate, not a diagnosis. BMI is only one piece of the picture — your pediatrician looks at growth trends over time, family history and overall health together.

How this is calculated

BMI itself is calculated the same way for kids as for adults: weight in kilograms divided by height in meters squared. What's different is how that number is interpreted. A BMI of 19 means something completely different for a 6-year-old than it does for a 16-year-old, because children's body composition changes constantly as they grow. That's why pediatric BMI is always reported as a percentile for age and sex rather than a flat category.

The official CDC BMI-for-age growth charts are built from large population surveys and plotted as smooth percentile curves (the well-known LMS statistical method) for boys and girls separately, covering ages 2 through 20. This calculator approximates those curves using representative reference points at each age and estimates where your child's BMI falls relative to that average, rather than reading the exact published chart — so treat the percentile here as a close estimate, not the precise clinical figure your pediatrician would plot.

The categories shown — underweight, healthy weight, overweight and obesity range — map to the same percentile thresholds pediatric guidance commonly uses: below the 5th percentile, 5th to under the 85th, 85th to under the 95th, and 95th and above, respectively.

Common edge cases & things to know

Percentile can shift up or down temporarily around growth spurts and puberty, since height and weight don't always increase in perfect sync — a single reading during a growth spurt isn't as meaningful as a trend over several checkups.

BMI doesn't distinguish between muscle and fat, so a lean, muscular or very athletic child can land in a higher percentile without it reflecting excess body fat. Conversely, a lower percentile isn't automatically a concern if a child is growing steadily along their own curve.

This tool covers ages 2–20 in line with the CDC reference range. For babies and toddlers under 2, growth is tracked against WHO growth standards instead — see the Baby & Toddler BMI Calculator.

A single BMI reading is a snapshot, not a diagnosis. Pediatricians typically care most about the trend across several well-child visits — whether a child is tracking steadily along their own curve over time — rather than any one number in isolation. A percentile that jumps unusually far up or down between visits is generally more worth discussing than where it sits on a given day.

Sources

BMI-for-age methodology and percentile categories referenced from the Centers for Disease Control and Prevention (CDC) growth charts, the American Academy of Pediatrics (AAP), and HealthyChildren.org.