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BMI / Body Mass Index

Body Mass Index (BMI) is a reliable indicator of body fatness for most people. BMI provides a simple numeric measure of a person's "fatness" or "thinness", allowing health professionals to discuss over-weight and under-weight problems more objectively with their patients. To calculate and interpret your individual BMI please use our BMI Calculator.

BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry. Therefore BMI can be considered a good alternative for direct measures of body fat.

However, BMI is not a diagnostic tool. For example, a person may have a high BMI, but to determine if excess weight is a health risk, a healthcare provider would need to perform further assessments. These assessments might include skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings.

BMI is calculated the same way for both adults and children. Hovewer the interpretation of BMI differs for adults and children:

BMI for Adults

For adults 21 years old and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women.

BMI for Children and Teens

For children and teens (2 to 20 years old), on the other hand, the interpretation of BMI is both age and sex specific. Instead of set thresholds for underweight and overweight, the BMI percentile allows comparison with children of the same sex and age. A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered overweight. Children with a BMI between the 85th and 95th percentile are considered to be at risk of becoming overweight. You can use PDP's BMI Calculator to calculate and interpret BMI values for your kids.

BMI interpretation tables

CategoryBMI range
StarvationLess than 16.5
UnderweightFrom 16.5 to 18.5
NormalFrom 18.5 to 25
OverweightFrom 25 to 30
Obese class IFrom 30 to 35
Obese class IIFrom 35 to 40
Obese class IIIGreater than 40

Table 1. BMI interpretation table for adults 21 y.o. and older
CategoryPercentile Range
UnderweightLess than the 5th percentile
Healthy weight5th percentile to less than the 85th percentile
At risk of overweight85th to less than the 95th percentile
OverweightEqual to or greater than the 95th percentile

Table 2. BMI interpretation table for children and teens from 2 to 20 y.o.

BMI for age percentiles

After BMI is calculated for children and teens, the BMI number is plotted on the BMI-for-age growth charts issued by Centers for Disease Control and Prevention (for either girls or boys) to obtain a percentile ranking. Percentiles are the most commonly used indicator to assess the size and growth patterns of individual children in the United States. The percentile indicates the relative position of the child's BMI number among children of the same sex and age. The growth charts show the weight status categories used with children and teens (underweight, healthy weight, at risk of overweight, and overweight).

Body Mass Index for age percentiles

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