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Kids' Questions About a Kid's BMI

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Nurse weighing tween boyEvery time you go for a check-up, does the nurse ask you to step on a scale to check your weight? Does she check your height to see how tall you are?

She's measuring to see how much you've grown. She uses your weight and height to figure out your BMI, which is short for body mass index. The nurse at your school might check your BMI, too.

What a Kid's BMI Shows

BMI is a way to measure how much body fat you have. Doctors check BMI because weighing too much for your height can cause health problems like a broken hip, knee pain, heart disease, or diabetes.

To find out your BMI, you need to know:

  • Your age
  • Your gender (whether you are a boy or girl)
  • Your height and weight

With this information, a nurse or doctor can look at a chart to find your BMI. There are also BMI calculators on web sites that anyone can use. Kids need a kid's BMI calculator that is different than the kind adults use.

Comparing Yourself to Other Kids

Kids' BMIs are a bit different from adult BMIs because most kids are still growing. Kids get a BMI percentile. A percentile tells you how your weight compares to kids like you -- the same age and gender. For example, a boy with a 75th BMI percentile is heavier than 75 out of 100 boys his age.

A high BMI (85th percentile or higher) means you weigh more than expected for your height. A low BMI means you weigh less than expected for your height. That's OK. You may be one of the lighter or one of the heavier kids in your age group. If your doctor thinks your weight could be a problem, he will talk with you and your parents about ways to make sure you are healthy.

What to Do About BMI

Remember that your body is growing and changing. That means the BMI you have now won't be the BMI that you'll have your whole life. You'll go through growth spurts, and your height and weight will change. As your body changes, your BMI will change, too.