BMI at age 17
This calculator places a BMI on the CDC growth chart for age 17. The sample is a boy at 5 ft 9 in and 144 lb, with a girl of the same age in the table.
How it works
First the page works out BMI: weight in kilograms divided by height in meters squared. Then it reads L, M and S from the CDC table for this age and sex. It finds z as ((BMI divided by M) to the power L minus 1) divided by (L times S) and turns z into a percentile. The table covers ages 2 to 20, and this male page sits at age 17.
Worked example
A boy aged 17 is 175.26 cm tall and weighs 65.317 kg. Square the height: 1.7526 × 1.7526 = 3.0716. Divide 65.317 by 3.0716 to get a BMI of 21.2648. The male table at this age has L -1.9491, M 21.242 and S 0.13306. 21.2648 divided by 21.242 = 1.001073. Raise 1.001073 to the power -1.9491 to get 0.997912. Subtract 1 to get -0.002088. -0.002088 divided by (-1.9491 × 0.13306) = 0.008. That z score is the 50th percentile, which is healthy weight.
At age 17, a boy and a girl each at the CDC median height and the weight that gives the median BMI. The form above is set to the boy.
- Male at median height and weight (5 ft 9 in, 144 lb)
- BMI 21.3, 50th percentile
- Female at median height and weight (5 ft 4 in, 122 lb)
- BMI 20.9, 50th percentile
Common questions
Why does a child BMI use percentiles and not the adult bands?
Children grow, and a healthy BMI changes with age and differs between males and females. A percentile shows where a child sits among others of the same age and sex. At age 17 the median BMI is 21.2 for males and 20.9 for females, and the example boy sits at the 50th percentile.
What do the percentile bands mean?
Below the 5th percentile is underweight. From the 5th up to the 85th is a healthy weight. From the 85th up to the 95th is overweight. The 95th and above is obesity. At age 17 the 5th, 85th and 95th percentile BMI values for males are 17.7, 24.9 and 28.3.
What is the median BMI at age 17?
On the CDC chart the median is 21.2 for males and 20.9 for females at age 17. The example BMI of 21.3 is 0.0 away from the male median of 21.2.
Does BMI show body fat in a child?
Only roughly. BMI uses height and weight. A muscular child can score high. A doctor looks at growth over time as well as the number. A BMI of 21.3 for this boy at age 17 says nothing about how much of the 144 lb is muscle.
Why does BMI change as a child grows?
BMI usually falls through early childhood and then rises through the teen years. That is normal growth, which is why the chart is built by age. The median BMI for males is 21.2 at age 17.