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Recommended BMI-for-age Cutoffs

BMI (kg/m2)Classification
≥ 95th percentileObese
85th to < 95th percentileOverweight
5th to < 85th percentileHealthy Weight
< 5th percentileUnderweight

In 2004, an expert committee (Barlow, 2007) comprised of representatives from 15 national health care organizations was convened and charged with revising the 1998 recommendations on the evaluation and treatment of child and youth obesity (Barlow and Dietz, 1998). The expert committee recommended classifying BMI at the 85th to 95th percentiles for age and sex to identify children or teens who are overweight, and a BMI greater than or equal to the 95th percentile to identify children or teens who are obese (Barlow, 2007). These cut points are unchanged from the 1998 expert committee recommendations (Barlow and Dietz, 1998).

  • The rationale for the use of these criteria is that a BMI at the 95th percentile in the U.S. population corresponds to a BMI of 30 in a young adult. In a young adult, a BMI greater than or equal to 30 is considered obesity.
  • A BMI at the 85th percentile in a young adult identifies a young adult with a BMI of 25, which is considered at the top end of a healthy weight classification.
  • Therefore, the criterion used for children and teens corresponds (roughly) to the criteria used for adults to identify overweight and obesity.

The cutoff for underweight of less than the 5th percentile of BMI-for-age is based on recommendations by the World Health Organization Expert Committee on Physical Status (World Health Organization, 1996).

 

Read More about adult BMI classifications

Classifications of Obesity, Overweight, and Underweight Adults

Classifications of obesity, overweight, and underweight are different for adults than for children and teens. For adults, obesity, overweight, and underweight categories are defined by fixed BMI cut points derived from morbidity and mortality data. Among adults, underweight and obesity, particularly higher levels of obesity, are associated with higher relative mortality risk compared with healthy weight (Flegal et al., 2013; Flegal et al., 2005). For adults, BMI is not age-or sex-specific as it is for children and teens.

Clinical guidelines for adult BMI classifications were established in 1998 by the National Heart, Lung, and Blood Institute in cooperation with The National Institute of Diabetes and Digestive and Kidney Disease (http://www.nhlbi.nih.gov/files/docs/guidelines/ob_gdlns.pdf) and are as follows:

 Obesity ClassBMI (kg/m2)
Underweight 18.5
Healthy weight 18.5 - 24.9
Overweight 25.0–29.9
ObesityI30.0–34.9
 II35.0–39.9
Extreme obesityIII≥ 40

Sensitivity, Specificity, and Validity of BMI-for-age as a Tool to Screen Children for Increased Adiposity

High BMI-for-age among children and teens correlates with excess adiposity (Mei et al 2002; Pietrobelli et al., 1998) and cardiovascular disease risk factors (Freedman and Sherry, 2009; Freedman et al., 2007). The accuracy of BMI-for-age as an indicator of body fatness varies according to the degree of body fatness, and “its accuracy increases with the degree of body fatness” (Freedman and Sherry, 2009; p. S27). Analyses of data from the Pediatric Rosetta Project showed that a high BMI-for-age (≥95th CDC percentile) is a good index of excess body fatness for both girls and boys (Freedman et al., 2005), and at the high BMI cut points (≥95th percentile), BMI-for-age has moderately high sensitivity and positive predictive values, as well as a high specificity for identifying children with excess body fatness (Freedman and Sherry, 2009, p. S31). Freedman, Wang, Thornton, and colleagues (2009) showed that levels of body fatness among children who had a BMI-for-age between the 85th and 94th percentiles are variable; only 30% of children classified as overweight have normal body fatness. Because BMI does not measure body fat directly and may lead to imprecise assessment of adiposity, BMI-for-age is not considered diagnostic of body fatness (Freedman, Wang, Thornton, et al., 2009). This is especially true for children classified as overweight.

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