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How the percentile was calculated
Every percentile calculator does this behind the scenes. Here is the same math, using your child's numbers and the CDC reference data.
Why teens don't use adult categories
During puberty, body fat and muscle change quickly, and differently for girls and boys. A BMI of 22 means something different at 13 than at 19. That's why BMI is judged by percentile until age 20:1
| Percentile | Category |
|---|---|
| Below the 5th | Underweight |
| 5th to below the 85th | Healthy weight |
| 85th to below the 95th | Overweight |
| 95th and above | Obesity |
At age 20, switch to the adult BMI calculator and adult categories.1
Teens and sports
Teens who train hard, especially in strength sports, can have a high BMI percentile because of muscle rather than fat. If that applies, waist size and how clothes fit are useful extra checks, and a doctor can assess body composition properly. BMI for athletes.
Talking with teens about BMI
Teens are often sensitive about weight. Keep conversations about energy, sleep, strength and food they enjoy, not numbers. Avoid comments about body shape.
Talk to a doctor if a teen seems preoccupied with weight, is skipping meals or is exercising compulsively. A doctor can also check a teen's growth and put their percentile in context. When to see a doctor.
Frequently asked questions
At what age do you use adult BMI?
At 20. The CDC BMI-for-age charts cover ages 2 through 19.2
Is BMI calculated differently for teens?
The formula is the same. Only the interpretation changes: a percentile for age and sex instead of adult categories. How BMI percentiles are calculated.
Why did my teen's BMI go up but their percentile stay the same?
BMI naturally rises through the teen years. Staying near the same percentile means they're growing along the same curve as before.
Is there a calculator for younger children?
Yes, the same calculator works from age 2: BMI for kids.
Sources
This page is for education and is not medical advice. A doctor can explain what a BMI percentile means for a teen's health and growth.
