Estimate a child's BMI and an approximate weight category for their age and sex. This is a general estimate, not a substitute for official growth charts.
For children and teens, BMI is calculated the same way as for adults, but it's interpreted differently — against age- and sex-specific percentile growth charts, because healthy body composition changes significantly as kids grow. A BMI number alone means little for a child without that percentile context.
BMI = (Weight in pounds × 703) ÷ (Height in inches)². This calculator then applies simplified, generalized age-adjusted BMI thresholds to estimate whether the result falls in the underweight, healthy weight, overweight, or obese range for the child's approximate age group.
A 10-year-old weighing 72 lb at 55 inches tall has a BMI of (72 × 703) ÷ 55² ≈ 16.6, which falls in the approximate healthy weight range for that general age bracket under this simplified model.
Real pediatric BMI assessment uses official CDC or WHO growth charts with precise LMS (Lambda-Mu-Sigma) percentile curves specific to each month of age and sex, which this simplified calculator does not replicate exactly. For an accurate percentile and any weight-related concerns, always consult your child's pediatrician, who can plot an exact result on the official growth chart used in clinical practice.
Their BMI (weight/height squared) is calculated first, then compared against CDC or WHO growth charts specific to their exact age and sex.
Children's healthy body composition changes constantly as they grow, so percentile-based comparison to same-age peers is far more meaningful than fixed adult cutoffs.
Discuss any concerns with your child's pediatrician — percentile trends over time and overall growth pattern matter more than a single reading.