Plotting and Interpreting BMI-for-Age

What to know

BMI-for-age can be plotted on growth charts. Percentile curves on the growth charts indicate the BMI-for-age percentile. This is the relative position of a child’s BMI to children of the same sex and age from the reference population used to create the growth charts.

A healthcare provider talking to a couple and their chlid.

Child and adolescent BMI categories

In children and adolescents 2 to 20 years old, BMI categories are based on BMI-for-age percentiles and defined as:

BMI Category

BMI Range

Underweight

Less than the 5th percentile

Healthy Weight

5th percentile to less than the 85th percentile

Overweight

85th percentile to less than the 95th percentile

Obesity

95th percentile or greater

Severe Obesity

120% of the 95th percentile or greater, or 35 kg/mor greater

Use the following case examples to practice plotting and interpreting BMI.

Case example 1: BMI-for-age

Name: Sam
Age: 9 years
Sex: boy
Height: 105.4 cm
Weight: 16.9 kg

Calculate BMI metrics

By-Hand Calculation: (16.9 kg / 105.4 cm / 105.4 cm) x 10,000 = 15.2
BMI: 15.2
BMI-for-age Percentile: 28th
Sam's doctor can use CDC's Child and Teen BMI Calculator to generate BMI.

BMI-for-Age Growth Chart

Because Sam’s BMI is below the 97th percentile for his age and sex, Sam’s doctor can plot his BMI on CDC’s BMI-for-Age Growth Chart.

BMI index for age percentiles from 2 to 20 years (boys)
Plot the intersection of age on the x-axis and BMI on the y-axis.

What does this mean?

Sam has a BMI of 15.2 kg/m2, placing him at the 28th percentile for age and sex. This means that Sam's BMI is greater than the BMIs of 28% of 9-year-old boys in the growth chart reference population.

Sam's BMI falls in the healthy weight category. The healthy weight category is defined as BMIs from the 5th percentile up to the 85th percentile for sex and age.

Case example 2: extended BMI-for-age

Name: Olivia
Age: 13 years
Sex: girl
Height: 60 inches
Weight: 175 pounds

Calculate BMI metrics

BMI: 34.2
Extended BMI-for-age Percentile: 99.2nd

Extended BMI-for-Age Growth Chart

Extended BMI-for-Age Growth Chart for girls ages 2–20
Because Olivia's BMI is above the 97th percentile for her age and sex, use CDC's Extended BMI-for-age growth Chart.

What does this mean?

Olivia has a BMI of 34.2 kg/m2, placing her at the 99.2nd percentile for age and sex. This means Olivia's BMI is greater than the BMIs of 99.2% of 13-year-old girls in the growth chart reference population.

Olivia's BMI of 34.2 kg/m2 is 130% of the 95th percentile, which is in the severe obesity category. This means that Olivia's BMI is 1.3 times higher than the BMI that is the 95th percentile for 13-year-old girls. BMIs at or above 120% of the 95th percentile for sex and age, or BMIs that are 35.0 kg/m2 or above, are in the severe obesity category.

Calculate and Plot BMI‎

To calculate and plot BMI metrics for patients, use CDC's Child and Teen BMI Calculator or use CDC's SAS Program or R Program.

Test your knowledge

  1. Which of the following is NOT true?
    1. If a 7-year-old girl’s BMI is at the 75th percentile for sex and age, it means her BMI is greater than the BMIs of 75% of 7-year-old girls in the growth chart reference population.
    2. Sex, age, height, and weight are all required to calculate BMI-for-age percentiles in children and adolescents.
    3. In children and adolescents, severe obesity is defined as BMI at or above 120% of the 95th percentile for age and sex, or BMI at or above 35 kg/m2.
    4. Extended BMI-for-Age Growth Charts should be used to plot and track the BMIs for all children and adolescents.

See answers.A

  1. Answer: D. CDC’s Extended BMI-for-age growth charts should be used to plot and track BMIs for children and adolescents with very high BMIs (above the 97th percentile for age and sex). These extended charts can help with conversations about growth and care between providers, patients, and patients’ families.