Guides
BMI for children and teens
Children grow, so the same number means different things at different ages.
For people under 18, BMI is compared with growth charts for the same age and sex and expressed as a percentile. The adult categories on this site do not apply to them, so this calculator is for adults only.
Why children are different
A child's body composition changes quickly with growth and puberty, and it differs between boys and girls. A BMI that is typical at 8 years old would be very different at 16. Percentile charts account for age and sex.
How it is assessed
Health professionals plot a child's BMI on a growth chart for their age and sex. In the CDC growth charts used in the United States, a BMI below the 5th percentile is underweight, from the 5th to below the 85th is healthy weight, from the 85th to below the 95th is overweight and the 95th or above is obesity. Other countries use WHO or national charts.
What to do
- Ask your pediatrician or family doctor to assess a child's growth.
- Focus on healthy habits for the whole family rather than a number.
- Do not use adult BMI categories for a child or teenager.
Frequently asked questions
At what age can the adult categories be used?
The adult categories are for people aged 18 and over. A health professional can advise for teenagers.