Child & Teen BMI Calculator

How to Calculate Child and Teen BMI

Body Mass Index (BMI) for children and teens is a measure used to assess body fatness. Unlike adult BMI, child and teen BMI is age- and sex-specific due to the changes in body composition during growth.

The BMI Formula

The formula for calculating BMI is the same for children and adults:

$$BMI = \frac{weight (kg)}{height (m)^2}$$

Where:

• BMI = Body Mass Index
• Weight is in kilograms (kg)
• Height is in meters (m)

Calculation Steps

1. Measure the child's weight in kilograms and height in meters.
2. Square the height.
3. Divide the weight by the squared height.
4. The result is the BMI.
5. Use CDC growth charts to determine the BMI percentile for the child's age and sex.

Example Calculation

Let's calculate the BMI for a 10-year-old boy with the following measurements:

• Weight: 35 kg
• Height: 1.4 m

Substituting these values into the formula:

$$\begin{align} BMI &= \frac{35}{1.4^2} \\ &= \frac{35}{1.96} \\ &= 17.86 \end{align}$$

The BMI for this child is 17.86. To interpret this value, we need to plot it on the CDC BMI-for-age percentile chart for boys. Let's assume this BMI corresponds to the 65th percentile for a 10-year-old boy.

Interpretation

The CDC defines the following weight status categories for children and teens:

• Underweight: Less than the 5th percentile
• Healthy weight: 5th percentile to less than the 85th percentile
• Overweight: 85th to less than the 95th percentile
• Obese: Equal to or greater than the 95th percentile

In our example, the 65th percentile falls within the "Healthy weight" category.

Visual Representation

This bar chart compares the example child's BMI percentile (65th) with the CDC's weight status categories. It visually demonstrates how the calculated BMI percentile relates to the different weight categories for children and teens.