The child BMI calculator computes BMI and age- and sex-specific percentile for children ages 2–18, following CDC growth chart standards. Child BMI interpretation differs from adults — a healthy range depends on age and sex.
Child BMI Percentile Calculator
Understanding Child BMI Percentiles
Unlike adult BMI, child BMI percentile must be interpreted relative to other children of the same age and sex. This is because normal body fat changes dramatically from age 2 to 18. An 8-year-old boy at the 75th percentile is in a healthy range; that same BMI value in an adult would be overweight.
CDC Growth Chart Categories
The CDC defines: Underweight = below 5th percentile; Healthy = 5th to 84th; Overweight = 85th to 94th; Obese = 95th and above. These categories are based on large US population samples. For international comparisons, the WHO growth reference may be more appropriate.
FAQ
Is this child BMI calculator free?
Yes, completely free. All calculations run locally in your browser.
What BMI percentile is healthy for a child?
For children 2-18, healthy weight is BMI between the 5th and 84th percentile. Underweight is below the 5th percentile. Overweight is 85th to 94th percentile. Obese is at or above the 95th percentile. Unlike adult BMI, children's BMI is age- and sex-specific because body fat levels change with age.
Is child BMI calculated the same as adult BMI?
The formula is the same — weight(kg) ÷ height(m)² — but interpretation is different. Adult BMI has fixed cutoffs (18.5, 25, 30). Child BMI is plotted on percentile curves that vary by age and sex, because what's normal body fat changes significantly from age 2 to 18.
How accurate is BMI for children?
BMI percentile is a useful screening tool but not a diagnostic measure. A child with high muscle mass may have elevated BMI without excess fat. BMI cannot distinguish fat from muscle. If a child is at or above the 85th percentile, a pediatrician should evaluate with additional assessments.
What should I do if my child's BMI is in the overweight range?
Consult your child's pediatrician before making dietary or activity changes. Children are still growing — restrictive dieting can harm development. Pediatricians typically recommend gradual lifestyle changes: more vegetables, less processed food, 60 minutes of physical activity daily, and limiting screen time.