Understanding BMI Percentiles
For adults, BMI is a fixed number. For kids, it changes with age. A 10-year-old boy with a BMI of 18 is considered "Healthy" (50th percentile), but a 20-year-old with a BMI of 18 is borderline "Underweight".
Because children grow at specific rates, we compare their BMI to other children of the exact same age and gender using Percentiles.
The 4 Growth Zones (CDC)
Underweight
May need nutritional support.
Healthy Weight
Target range for optimal health.
Overweight
Monitor lifestyle habit changes.
Obesity
High risk of metabolic issues.
CDC vs. WHO Charts
- 👶
0 - 2 Years: Use WHO
The World Health Organization (WHO) standards reflect the growth of breastfed infants, which is the gold standard for early development.
- 🧒
2 - 20 Years: Use CDC (This Tool)
The CDC methodology is designed to track growth through childhood and puberty across the diverse US population.
Frequently Asked Questions
My child is in the 90th percentile. Is that bad?
Why is adult BMI inaccurate for children?
Does muscle mass affect this score?
When should I use the WHO chart instead?
What is a Z-Score?
Tools & Data Verified by the EverydayCalculators Medical Research Team.
Last updated: January 2026.