Body mass index (BMI) is a calculation that uses height and weight to estimate
how much body fat someone has. You can use the KidsHealth BMI calculator below to
find your child's BMI. But it's also important to talk to your
child's doctor to help understand the results.
Starting when your child is 2 years old, the doctor will determine BMI at all routine
checkups. Because BMI
changes with age, doctors plot children's BMI measurements on standard gender-specific
growth charts. Over
several visits, the doctor is able to track your child's growth pattern.
Although not a perfect measure of body fat, BMI helps identify children who are
gaining weight too slowly or too quickly.
What Do the Figures Mean?
BMI percentiles show how a child's measurements compare with others the same gender
and age. For example, if a child has a BMI in the 60th percentile, 60% of the kids
of the same gender and age who were measured had a lower BMI.
BMI is not a direct measure of body fat. Kids can have a high BMI if they have
a large frame or a lot of muscle, not excess fat. And a kid with a small frame may
have a normal BMI but still can have too much body fat.
BMI is less accurate during puberty.
It's common for kids to gain weight quickly — and see their BMI go up —
during puberty. Your doctor can help you figure out whether this weight gain is a
normal part of development or whether it's something to be concerned about.
The categories that describe a person's weight are:
Underweight: BMI is below the 5th percentile age, gender, and
Healthy weight: BMI is equal to or greater than the 5th percentile
and less than the 85th percentile for age, gender, and height.
BMI is at or above the 85th percentile but less than the 95th percentile for age,
gender, and height.
Obese: BMI is at or above the 95th percentile for age, gender,
It's important to look at the BMI as a trend instead of focusing on individual
numbers. Any one measurement, taken out of context, can give you the wrong impression
of your child's growth.
While BMI is an important indicator of healthy growth and development, BMI is not
a perfect measure of body fat. If you're concerned that your child may be gaining
or losing weight too fast, talk to your doctor.