BMI for Children and Teens
A child's BMI is read against growth charts, not the adult scale. Here is how that works and why the same number means different things at different ages.
You cannot hand a seven-year-old the adult BMI chart. Children grow at very different rates, and a body that looks heavy at age six may be perfectly average by age twelve. Pediatricians therefore compare a child with other children of the same age and sex, using growth charts published by the Centers for Disease Control and Prevention.
Percentiles, not categories
A percentile tells you where a child stands relative to 100 children of the same age and sex. The 60th percentile for BMI means the child's BMI is higher than 60 of those children. The categories pediatricians use are built on those percentiles:
| Percentile | Category |
|---|---|
| Below the 5th | Underweight |
| 5th to under the 85th | Healthy weight |
| 85th to under the 95th | Overweight |
| 95th and above | Obese |
Notice that there is no single BMI number that defines a healthy child. A BMI of 18 might be near the 85th percentile for a six-year-old and near the 50th for a fifteen-year-old. That is why the adult calculator on this site should not be used for anyone under 20.
What parents should take from the number
A single measurement tells you very little. A pattern over time tells you a lot. Children normally gain weight before a growth spurt, so a brief rise in BMI is often followed by a drop as height catches up. What concerns pediatricians is a percentile that keeps climbing across several visits, or one that crosses two major lines on the chart.
Do not put a child on a diet
Restricting calories in growing children can interfere with growth, bone development and eating habits that last a lifetime. When a pediatrician recommends action, it is usually about the whole family's patterns: more movement, fewer sugary drinks, more sleep, and meals eaten together. Talk to your child's doctor before changing anything.
Why the CDC charts are used instead of the WHO charts
The World Health Organization publishes growth standards for children from birth to age two that describe how healthy children should grow under ideal conditions. The CDC charts, used from age two onward in the United States, describe how a representative sample of American children actually grew. For most of childhood the two agree closely; where they differ, US pediatricians follow the CDC.
Adults can use the calculator
For anyone 20 or older, the standard BMI categories apply. Start with the BMI calculator, then look at the BMI chart if you want to see the boundaries laid out by height.