A child's BMI

Measuring body mass index (BMI)

Body mass index (BMI) is a calculation that uses your child’s height and weight to estimate how much body fat he has. Your doctor uses BMI to determine whether your child is the appropriate weight for his age and height.

From the age of 2 years, a BMI check forms part of your child’s regular checkups. The doctor checks your child’s BMI against other children and then puts the measurements on a standard child growth chart. There are separate charts for boys and girls to account for growth and body fat differences. After several checks, a pattern emerges and your doctor can track your child’s growth.

BMI can be a helpful measurement if your child’s at risk of becoming overweight as he gets older. In older children, there’s a strong link between BMI and body fat. A child with higher BMI readings will probably have weight problems when he’s older. If your child has high BMI readings, take steps to change his diet and exercise habits. BMI isn’t a perfect measurement. Children gain weight quickly – for example, during puberty – and a high BMI may be due to a high muscle mass. Monitor BMI as a trend rather than individual numbers.