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Child BMI Calculator.

Pediatric BMI with CDC growth chart percentile interpretation for children and teens aged 2–20.

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This tool provides estimates for educational purposes. Consult your child's pediatrician for clinical growth assessment and guidance.

BMI

CDC Category

This calculator covers ages 2–20. For infants under 2, use WHO weight-for-length charts.

Runs entirely in your browser. The values you enter never leave your device — there is no request to our server and nothing is stored. How we handle data

Child BMI vs Adult BMI

The BMI formula is the same for children and adults — weight in kg divided by height in meters squared. What differs is how the result is interpreted. Children's body fat percentage naturally changes as they age and differs between boys and girls, so a fixed BMI threshold cannot be used. Instead, BMI is compared to age-and-sex-specific reference data from CDC growth charts.

CDC Percentile Categories

▪ Below 5th percentile — Underweight
▪ 5th to 84th percentile — Healthy weight
▪ 85th to 94th percentile — Overweight
▪ 95th percentile or above — Obese
Knowledge Base

Understanding Pediatric BMI and Growth Percentiles Methodology.

Child BMI uses the same formula as adult BMI (weight ÷ height²) but interprets the result using age-and-sex-specific percentile charts. A BMI of 18 means something very different for a 5-year-old girl than a 14-year-old boy — which is why fixed adult thresholds (18.5, 25, 30) do not apply to children.

The Calculation Branch

BMI = weight (kg) ÷ height (m)² | Then compare to CDC growth chart for child's age and sex to find percentile

Industrial Standards.

Percentile data is derived from CDC BMI-for-age growth charts (2000 revision), based on data from the National Health and Nutrition Examination Survey (NHANES). The percentiles show where a child falls relative to other children of the same age and sex in the US reference population.

In-Depth Analysis & Reference Data

BMI is a screening tool, not a diagnostic one. A child whose BMI plots in the overweight or obese range should be evaluated by a pediatrician who can account for muscle mass, bone structure, ethnicity, and growth trajectory. A single BMI measurement is less meaningful than tracking BMI over time to see if a child is following a consistent growth percentile.

Registry Questions & FAQ.

Is BMI a reliable indicator for children?

BMI-for-age is a reasonable screening tool at the population level but has limitations for individuals. Muscular children can have high BMI without excess body fat. Ethnicity also affects the relationship between BMI and actual body fat percentage. Pediatricians consider BMI alongside weight history, diet, activity level, and family health history.

How often should I check my child's BMI?

The American Academy of Pediatrics recommends BMI screening at every annual well-child visit from age 2 onward. Tracking the percentile over multiple years is more useful than a single reading — a child consistently at the 70th percentile is not a concern; a child who jumps from the 50th to the 90th percentile in one year warrants further discussion.

All metrics verified against ISO/ASTM benchmarks.