BMI at age 7
Adult BMI bands do not apply at age 7. The form below gives a percentile for age and sex, and the example walks through one case.
How it works
BMI is weight in kilograms divided by height in meters squared. For a child that number is scored against the CDC table. M is the median BMI for the age and sex. L and S set the shape of the spread. The z score and percentile follow from all three. The table covers ages 2 to 20, and this male page sits at age 7.
Worked example
For a boy aged 7 at 4 ft 0 in and 51 lb, height is 1.2192 m and weight is 23.133 kg. Square the height: 1.2192 × 1.2192 = 1.4864. BMI is 23.133 divided by 1.4864, which is 15.5631. The CDC values are L -3.3232, M 15.513 and S 0.09213. Divide the BMI by M to get 1.003230. Raise that to the power L to get 0.989341. Subtract 1 to get -0.010659. Divide by L × S to get z = 0.035. The 51st percentile falls in the healthy weight band.
At age 7, 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 (4 ft 0 in, 51 lb)
- BMI 15.6, 51st percentile
- Female at median height and weight (4 ft 0 in, 51 lb)
- BMI 15.6, 53rd percentile
Common questions
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 7 the 5th, 85th and 95th percentile BMI values for males are 13.7, 17.4 and 19.2.
What is the median BMI at age 7?
On the CDC chart the median is 15.5 for males and 15.5 for females at age 7. The example BMI of 15.6 is 0.0 away from the male median of 15.5.
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 15.6 for this boy at age 7 says nothing about how much of the 51 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 15.5 at age 7.
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 7 is 17.4.