Teen BMI calculator
Enter an age, a sex, a height and a weight to see BMI for age. The example below uses a girl aged 16 at 5 ft 4 in and 119 lb.
How it works
There are three steps. Work out BMI. Read L, M and S from the CDC table for the age and sex. Then find z with ((BMI divided by M) to the power L minus 1) divided by (L times S) and convert z to a percentile. For females at age 16 the median is M 20.453.
Worked example
For a girl aged 16 at 5 ft 4 in and 119 lb, height is 1.6256 m and weight is 53.977 kg. Square the height: 1.6256 × 1.6256 = 2.6426. BMI is 53.977 divided by 2.6426, which is 20.4257. The CDC values are L -2.1192, M 20.453 and S 0.14909. Divide the BMI by M to get 0.998665. Raise that to the power L to get 1.002835. Subtract 1 to get 0.002835. Divide by L × S to get z = -0.009. The 50th percentile falls in the healthy weight band.
At age 16, 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 girl.
- Male at median height and weight (5 ft 8 in, 135 lb)
- BMI 20.5, 50th percentile
- Female at median height and weight (5 ft 4 in, 119 lb)
- BMI 20.4, 50th percentile
Common questions
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 females is 20.5 at age 16.
What should I do if my child is above the 85th percentile?
One reading is not a diagnosis. Raise it with your child's doctor, who can look at growth history and the whole picture. The 85th percentile BMI for females at age 16 is 24.7.
Which ages does this calculator cover?
It covers ages 2 to 20, the range of the CDC growth charts. For adults over 20 use the adult BMI calculator. This page reads the CDC female table at 192.5 months.
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 16 the median BMI is 20.6 for males and 20.5 for females, and the example girl 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 16 the 5th, 85th and 95th percentile BMI values for females are 16.8, 24.7 and 28.9.