Understanding BMI for Obesity Awareness

Body Mass Index Basics

A doctor measuring a child's weight.
Your pediatrician should measure your child's BMI at each checkup.. Photo by Getty Images

Although BMI has been used in Pediatricians since 1991, it wasn't until their 2003 policy statement on the Prevention of Pediatric Overweight and Obesity, that the American Academy of Pediatrics called on doctors to begin routinely calculating a child's body mass index or BMI to help in the early recognition of childhood obesity.

So now, in addition to plotting a child's height and weight on his growth chart, their BMI should also be charted each year.

What is BMI?

BMI is calculated with a child's height and weight using a simple formula, a BMI calculator, or by looking it up on a BMI wheel or BMI tables. Although it doesn't measure body fat, BMI can be used to determine if a child is overweight.

BMI is usually thought of as a tool that is used in treating children who are overweight, however, it can also help determine if children are underweight if they have a low BMI.

Understanding BMI

In adults, once you calculate your BMI, it is rather easy to interpret your results, as a BMI between 25 to 30 is considered overweight and a BMI of 30 and above is considered obese.

Interpreting BMI is a bit more complicated for children, though, since you also have to take into account the child's age to figure out the percentile ranking for that BMI from a girl or boy's BMI growth chart. This BMI percentile can then help you determine if a child is overweight or at a healthy weight.

At Risk of Overweight???

Adding to the confusion a little more, instead of classifications for overweight and obese, as we have for adults, there used to be an 'At Risk of Overweight' category for kids.

The 'At Risk of Overweight' category was especially confusing. Many people interpreted that to mean that their child was at a healthy weight and 'might' become overweight later.

That category really corresponded to the adult overweight category, though, and the child overweight category corresponded to the adult obese category.

To be diplomatic, experts decided to soften the terms of the BMI categories for kids and left out the word obese.

The 'At Risk of Overweight' category was removed in 2007.

BMI Categories

The BMI categories are now the same as they are for adults, including that kids can be:

  • Underweight - BMI less than the 5th percentile
  • Healthy Weight - BMI 5th percentile up to the 85th percentile
  • Overweight - BMI 85th to less than the 95th percentile
  • Obese - BMI greater than or equal to the 95th percentile

Do you know how to figure out if your child is at a healthy weight?


American Academy of Pediatrics. Prevention of Pediatric Overweight and Obesity. PEDIATRICS Vol. 112 No. 2 August 2003, pp. 424-430

Klein et al. Adoption of Body Mass Index Guidelines for Screening and Counseling in Pediatric Practice. Pediatrics . 2010;125(2).

Krebs et al. Assessment of child and adolescent overweight and obesity. Pediatrics. 2007;120(suppl 4):S193–S228

Ogden, et al. Changes in Terminology for Childhood Overweight and Obesity. National Health Statistics Report. Number 25. June 25, 2010.

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