IS YOUR CHILD OVERWEIGHT? HOW TO USE THE BODY MASS INDEX (BMI) TOOL

IS YOUR CHILD OVERWEIGHT? HOW TO USE THE BODY MASS INDEX (BMI) TOOL

One of the hardest parts of my job is telling parents and patients bad news. No one wants to be the bearer of bad news. Far and away, the most common bad news I bear is that a child is overweight. It doesn’t exactly make you beloved to say, “Your child is overweight.” However, I think that potential consequences of not saying anything are too great. Kids who are overweight usually turn into adults who are overweight. Overweight kids are at increased risk of developing heart disease, type 2 diabetes, high cholesterol, high blood pressure, and the list goes on and on. So if I can help course-correct while kids are still at a young age, I can truly prevent a lot of medical problems.

One of the most widely used measures of size is the Body Mass Index or BMI. BMI is a simple calculation that utilizes weight and height. Now I know and acknowledge that the measure has shortcomings (it doesn’t take into account body build or fat vs. muscle), but it can aid in helping determine if there is a problem. In general, the higher numbers are bad.

How to calculate a BMI

When you take your child to the pediatrician for a well-child exam, she should tell you your child’s BMI (in my office, I give them in all well visits over the age of 2). If however, you’d like to calculate it yourself, it is easy enough to do (with a calculator).

  1. Multiply your child’s weight (in pounds) by 703=A
  2. Multiply your child’s height (in inches) by itself=B
  3. Divide A by B

Example, Pat weighs 165 lbs and is 63 inches tall:  

A=(165 x 703) 115,995

B=(63 x 63) 3,969

BMI= (115,995/3,969) 29.2

What do the BMI results mean?

The official BMI cutoffs (according to the CDC and AAP) are based on percentiles. Using the percentile charts allows correction for age rather than using an absolute number.

  • Less than 5% BMI = underweight
  • 5-85% BMI = healthy weight
  • 85-95% BMI = overweight
  • Greater than 95% BMI = obese

In a young adult, these numbers roughly correspond to a BMI greater than 25% as being overweight, and a BMI greater than 30% as being obese (in young adults).

Please don’t be upset when your pediatrician tells you that your child is overweight. She’s telling you because she cares about your child’s health and wants, as you do, for your child to live a long healthy life.

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About The Author

Dr. Monica Wonnacott

I'm a pediatrician and a mom. I've been doing this doctor thing for 10 years, and love it. I'm known for giving parents the straight scoop without always sugar-coating it. And I believe in educating parents. The more you know, the better care you give your kids.

Dr. Monica Wonnacott


I'm a pediatrician and a mom. PediatricAnswers.com is my blog where parents can get the straight scoop on their child's health, largely based on my experience in the office and at home. I don't diagnose on the site, so please don't ask. These are just my opinions. Use this site as a resource. And trust your parent gut.

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