BMI for Children and Teens
For ages 2 to 19, BMI is read by percentile, not the adult categories.
BMI uses the same height-and-weight formula for everyone, but for children and teenagers the result means something different. A growing child's healthy BMI changes with age and differs between girls and boys, so the number is compared with others of the same age and sex as a percentile, not the fixed adult bands.
Calculate the BMI number
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For an accurate percentile, use the growth charts from your pediatrician or a health authority such as the WHO: WHO growth references for ages 5 to 19.
Why children and teens are different
An adult BMI of 19 counts as a healthy weight, but the same 19 could be high for a 6-year-old and low for a 17-year-old. That is why a clinician reads a child's BMI on a growth chart as a percentile, for example in the 60th percentile, which accounts for their age and sex. The fixed adult underweight and overweight labels simply do not fit a still-growing body.
Frequently asked questions
What is a healthy BMI for a child?
There is no single number. A healthy BMI for a child or teen falls roughly between the 5th and 85th percentile for their age and sex, read from a growth chart. Below the 5th is usually counted as underweight and above the 85th as overweight, but only a percentile chart, or a pediatrician, can place your child correctly.
Why can I not use the adult BMI categories for my child?
Because children are still growing, and the amount of body fat that is healthy changes a lot with age and differs between girls and boys. The adult thresholds (18.5, 25 and 30) are fixed and would mislabel most children. A percentile compares your child with others of the same age and sex instead.
At what age do the adult BMI categories apply?
From age 20. For 20 and over, the standard adult BMI calculator and categories apply. For ages 2 to 19, use a percentile growth chart with a clinician.