Child BMI Calculator
Find a child's or teen's BMI-for-age percentile and weight category using CDC growth charts.
About the Child BMI Calculator
Children's body fat changes with age and differs by sex, so BMI is compared with others of the same age and sex using the CDC 2000 BMI-for-age charts (ages 2–20). Categories: below the 5th percentile underweight, 5th to below 85th healthy, 85th to below 95th overweight, 95th and above obesity. BMI is a screening tool, not a diagnosis.
The formula
BMI = kg ÷ m²; percentile from CDC LMS: z = ((BMI ÷ M)^L − 1) ÷ (L × S)
Worked example
Example: BMI-for-age = 12.3rd percentile
- Inputs: Sex: Girl; Age: 11 years; Units: lb / in; Height: 61 cm or in; Weight: 80 kg or lb.
- Formula: BMI = kg ÷ m²; percentile from CDC LMS: z = ((BMI ÷ M)^L − 1) ÷ (L × S)
- Result: BMI-for-age = 12.3rd percentile
Questions people ask
Why not use adult BMI categories?
Healthy BMI changes a lot through childhood and puberty.
Why does child BMI use percentiles?
Children's body fat changes as they grow and differs between boys and girls, so a child's BMI is compared with others of the same age and sex instead of fixed adult cut-offs.