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	Endothelial Assessment of Risk from Lipids in Youth	University of California, San Francisco

Body Mass Index (BMI)

Your Body Mass Index (BMI) is a number that shows how your weight compares to your height.  BMI indicates how thin or how fat you are (unless you are very muscular, in which case BMI is not accurate). The higher the BMI the more fat you have compared to your height.

General formula for calculating BMI:    BMI = weight / height²

What is the BMI number that indicates you are overweight?  In adults a BMI over 25 is considered overweight. But in kids the overweight BMI number is not the same as in adults, and is not even the same for kids of different ages.  Therefore, it is important to use a BMI calculator especially for kids, and to also use what is called the BMI percentile chart.  The BMI percentile chart works for all ages, and avoids having to have a separate BMI chart for each age child.  Your BMI percentile shows how your BMI compares to other kids else your age and sex.  For example, if your BMI is 24 and is 80th percentile for your age, that means your BMI is 80th compared to 100 typical kids your age and sex.

Why is BMI percentile important?  Because BMI percentile is related to health risks. And most importantly, the overweight and underweight BMI percentile values are the same for all ages.

• BMI less than 5th percentile: Underweight
• BMI greater than 85th percentile: At Risk of Overweight
• BMI greater than 95th percentile: Overweight
• BMI between 5th and 85th percentile: Healthy Weight

Therefore, if your BMI is in either the top or bottom 5 percent, you have health risks due to your weight.

Your BMI, height, and weight percentiles show how you compare to everybody else. For example, if you are 50th percentile in height that means that you are taller than 50 out of 100 typical kids your age and sex.  If you are 80th percentile in weight that means you are heavier than 80 out of 100 kids your age and sex, according to the CDC National Health Center for Statistics.

How is BMI related to health risks?

• Six out of ten children and teens with a BMI above the 95th percentile have at least one risk factor for cardiovascular disease while 2 out of 10 have two or more risk factors for cardiovascular disease.
• Overweight children are likely to become overweight adults.

Source:  Guidelines of the US Center for Disease Control Expert Committee on Overweight in Children and Adolescents.

BMI Calculator for Kids

Use this calculator to find the Body Mass Index (BMI) percentile for a child aged 2-20.

• BMI Percentile Calculator (for kids) (opens in a new window)

Source:  Blubber Busters.com website (http://www.blubberbuster.com/height_weight.html) 2003.

BMI Calculator for Adults

Use this calculator to find the Body Mass Index (BMI) for an adult.

• BMI Calculator (for Adults)

Source:  US Center for Disease Control (CDC).

Growth Charts

Below are links to the new CDC child/adolescent growth charts on which our calculator is based (requires Adobe Acrobat Reader to view).  The calculator for kids uses the actual CDC-supplied data files of these growth charts.

• Weight-for-age percentiles: Girls, 2-20 years
• Height-for-age percentiles: Girls, 2-20 years
• BMI-for-age percentiles: Girls, 2-20 years



• Weight-for-age percentiles: Boys, 2-20 years
• Height-for-age percentiles: Boys, 2-20 years
• BMI-for-age percentiles: Boys, 2-20 years

Revised:  16 July 2003

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For more information, contact:  marguerite.engler@nursing.ucsf.edu           Version 1.7 · 17 Jan. 2006