Understanding BMI in Children

How is the BMI Percentile calculated?

Unlike adults, children's BMI must be compared to growth charts because body fat changes with age and differs significantly between boys and girls. For children and teens, BMI is age- and sex-specific and is often referred to as BMI-for-age.

BMI = weight (kg) / [height (m)]²

Using the Percentile Calculator: an example

Consider a 10-year-old boy measuring 54 inches and 70 lbs. To determine his weight status, his BMI must be calculated and then compared to the growth standard for his specific age and gender group.

Step-by-step calculation:

• Calculating the BMI of 16.9.
• Plotting it on the CDC growth chart for 10-year-old boys.
• Identifying the 65th percentile rank.

Weight Status Categories

Health categories are based on the following percentile ranges: Underweight (<5th percentile), Healthy (5th to <85th percentile), Overweight (85th to <95th percentile), and Obese (≥95th percentile).

Frequently Asked Questions

Is BMI a diagnostic tool? No. BMI is a screening tool used to identify potential weight issues. A healthcare provider would need to perform further assessments to determine if excess fat is a health concern.

Why isn't adult BMI used for kids? Children's body composition varies as they grow, and it differs by sex. Adult BMI categories do not account for these developmental factors.

What is a BMI percentile? A percentile rank shows how a child's BMI compares to other children of the same age and sex from a reference population.