BMI is Used Differently with Children Than it is With Adults

In children and teens, body mass index is used to assess underweight, overweight, and risk for overweight. Children's body fatness changes over the years as they grow. Also, girls and boys differ in their body fatness as they mature. This is why BMI for children, also referred to as BMI-for-age, is gender and age specific.^{1, 2} BMI-for-age is plotted on gender specific growth charts. These charts are used for children and teens 2 – 20 years of age.

Each of the CDC BMI-for-age gender specific charts contains a series of curved lines indicating specific percentiles. Healthcare professionals use the following established percentile cutoff points to identify underweight and overweight in children.

	Underweight	BMI-for-age < 5th percentile
	At risk of overweight	BMI-for-age 85th percentile to < 95th percentile
	Overweight	BMI-for-age > 95th percentile

 

BMI decreases during the preschool years, then increases into adulthood. The percentile curves show this pattern of growth.

What does it mean if my child is in the 60th percentile? The 60th percentile means that compared to children of the same gender and age, 60% have a lower BMI.

Example
Let's look at the BMI for a boy as he grows. While his BMI changes, he remains at the 95th percentile BMI-for-age.

Age BMI Percentile 2 years 19.3 95th 4 years 17.8 95th 9 years 21.0 95th 13 years 25.1 95th

We see how the boy's BMI declines during his preschool years and increases as he gets older.

Why is BMI-for-age a useful tool?
BMI-for-Age is used for children and teens because of their rate of growth and development. It is a useful tool because

• BMI-for-age provides a reference for adolescents that can be used beyond puberty.
• BMI-for-age in children and adolescents compares well to laboratory measures of body fat.
• BMI-for-age can be used to track body size throughout life.

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