Body Mass Index (BMI)-for-age

Body mass index (BMI) is a calculation used for children over age 2 years. It is expressed as a ratio of weight (in kg) to height (in m) squared:

BMI can be obtained with a number of methods:

• (weight in kg) / (height in m) / (height in m)
• [(weight in pounds) / (height in inches) / (height in inches)] x 703
• BMI tables, downloaded from the CDC website: www.cdc.gov/nccdphp/dnpa/growthcharts/bmi_tools.htm
• BMI calculator, available on the CDC website: www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi.htm

BMI-for-age is plotted on sex-specific charts to describe a child's weight and height proportionality, and can be used to monitor changes over time.

BMI has been shown to be a good indicator of obesity and risk for obesity in children and adults.

• BMI-for-age between the 85th and 94th percentiles is indicative of overweight (previously noted as “at risk of overweight”)
• BMI-for-age at or above the 95th percentile is indicative of obesity

There are fewer data to support the use of BMI for age as an indicator of underweight than overweight. The guideline is:

• Underweight is indicated by a BMI-for-age less than the 5th percentile

Changes in percentile channels can also indicate nutritional risk.