Health
Child BMI Percentile Calculator
Find a child's BMI and CDC growth-chart percentile for ages 2 to 20. Uses age and sex specific cutoffs (5th, 85th, 95th) from the CDC 2000 reference data, not adult BMI bands.
Child measurements
Enter age (2 to 20), sex, weight, and height to see the BMI percentile.
Pediatric BMI applies to children and teens aged 2 to 19. Results use CDC Year-2000 BMI-for-age growth charts. This is an estimate, not a diagnosis. Talk to a pediatrician about your child's growth.
Frequently Asked Questions about the Child BMI Percentile Calculator
Why does pediatric BMI use percentiles instead of the adult cutoffs?
Children's bodies change rapidly with age, and average BMI shifts dramatically between age 5 and age 15. The adult cutoffs (under 18.5, 18.5 to 24.9, 25 to 29.9, 30 plus) were derived for adults whose body composition is stable, so applying them to a child mislabels healthy growth as underweight or overweight. Pediatric BMI compares a child to other children of the same age and sex, expressed as a percentile, which is why the same BMI of 17 can be healthy for one age and concerning for another.
What CDC growth chart data does this calculator use?
The calculator uses the CDC Year-2000 BMI-for-age growth charts (NCHS, May 2000), the standard pediatric reference in US clinical practice for ages 2 to 19. It looks up the 5th, 85th, and 95th percentile cutoffs for the child's exact age in months and sex, then places the child's BMI inside that band. CDC and the AAP both recommend these charts for screening overweight and obesity in children and teens.
Why does the calculator only work from age 2?
For infants and toddlers under age 2, the World Health Organization (WHO) growth standards are the recommended reference, not BMI-for-age. CDC and AAP guidelines tell clinicians to use WHO weight-for-length and length-for-age charts up to 24 months, then switch to the CDC BMI-for-age chart from age 2 onward. Asking about BMI for a 1-year-old would return a value the formula technically computes but that no pediatric guideline interprets, so this calculator rejects ages under 2.
What do the four weight categories mean?
CDC classifies pediatric BMI into four bands by percentile: underweight is below the 5th percentile, healthy weight is the 5th up to under the 85th, overweight is the 85th up to under the 95th, and obese is the 95th percentile or above. These are screening categories, not diagnoses. A child near a cutoff or with a sudden percentile change should be evaluated by a pediatrician rather than acted on from a single calculator result.
Why can a BMI of 20 be obese for a 6-year-old but normal for an adult?
At age 6, the 95th percentile BMI for a boy is roughly 18, so a BMI of 20 sits well above that cutoff and lands in the obese band. For an adult, 20 is comfortably inside the healthy 18.5 to 24.9 range. Adult and child reference populations are completely different: average BMI dips during early childhood, hits its low around age 5 to 6, then rises through puberty into adulthood. That is why pediatric BMI is always read against age-and-sex matched peers, not the adult scale.