BMI at age 5
Enter an age, a sex, a height and a weight to see BMI for age. The example below uses a boy aged 5 at 3 ft 7 in and 41 lb.
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. For males at age 5 the median is M 15.419.
Worked example
A boy aged 5 is 109.22 cm tall and weighs 18.597 kg. Square the height: 1.0922 × 1.0922 = 1.1929. Divide 18.597 by 1.1929 to get a BMI of 15.5897. The male table at this age has L -2.6152, M 15.419 and S 0.07599. 15.5897 divided by 15.419 = 1.011071. Raise 1.011071 to the power -2.6152 to get 0.971617. Subtract 1 to get -0.028383. -0.028383 divided by (-2.6152 × 0.07599) = 0.143. That z score is the 56th percentile, which is healthy weight.
At age 5, 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 (3 ft 7 in, 41 lb)
- BMI 15.6, 56th percentile
- Female at median height and weight (3 ft 7 in, 40 lb)
- BMI 15.2, 52nd 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 males is 15.4 at age 5.
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 males at age 5 is 16.8.
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 male table at 60.5 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 5 the median BMI is 15.4 for males and 15.2 for females, and the example boy sits at the 56th 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 5 the 5th, 85th and 95th percentile BMI values for males are 13.8, 16.8 and 17.9.