BMI for Children and Teens: Why Percentiles Replace the Adult Ranges
October 21, 2026
For people aged 2 to 19, BMI is interpreted as a percentile compared with other children of the same age and sex, not with the fixed adult ranges. The CDC classes a BMI-for-age below the 5th percentile as underweight, the 5th to under the 85th as healthy weight, the 85th to under the 95th as overweight, and the 95th or above as obesity. The calculation itself is the same as for adults: weight in kilograms divided by height in meters squared.
Skip the math and get your answer instantly:
Open the BMI Calculator →Why Percentiles?
Children's body fat changes substantially as they grow, and it differs between boys and girls at the same age. A BMI of 18 might be ordinary for a 14-year-old and high for a 6-year-old. Comparing against growth-chart reference data accounts for that.
A percentile of 70 means the child's BMI is higher than 70% of the reference group of the same age and sex.
CDC Weight Status Categories
The cutoffs are used for screening, not diagnosis. A high percentile prompts a closer look by a pediatrician, who may consider growth patterns, family history, and diet.
| BMI-for-age percentile | Category |
|---|---|
| Below 5th | Underweight |
| 5th to below 85th | Healthy weight |
| 85th to below 95th | Overweight |
| 95th or above | Obesity |
How Parents Should Use It
A single measurement is less informative than the trend. Children can cross percentile lines during growth spurts, and a steady track along a percentile curve is usually reassuring.
Weight talk can be sensitive, so focus on habits like regular meals, sleep, activity, and limiting sugary drinks rather than on the number. If you are concerned, ask your pediatrician to plot your child's BMI on a growth chart.
Frequently Asked Questions
Can I use the adult BMI chart for my child?
No. Use BMI-for-age percentiles, because normal BMI changes with age and differs between boys and girls.
What BMI percentile is healthy for a child?
The CDC defines healthy weight as the 5th to less than the 85th percentile.
How is a child's BMI calculated?
Using the same formula as adults, weight in kg divided by height in meters squared, then plotted on a BMI-for-age chart.
Is a high BMI percentile a diagnosis?
No. BMI is a screening tool. A pediatrician decides whether further assessment is needed.