Body Mass Index (BMI) is calculated the same way for everyone, regardless of age: it’s your weight in kilograms divided by the square of your height in meters (kg/m²). However, the interpretation of BMI values does depend on age, especially for children and teenagers.
For Adults (ages 20 and over): The BMI categories (underweight, normal weight, overweight, and obesity) are standardized and do not vary with age or sex. An adult’s BMI is interpreted using the same scale regardless of their age.
For Children and Teenagers (ages 2 to 19): BMI is age and sex-specific because children’s body composition varies as they grow. In this age group, BMI percentiles are used instead of fixed categories. These percentiles compare a child’s BMI with that of other children of the same age and sex. For example, a child in the 85th percentile weighs more than 85% of children their age and sex.
Why Age Matters for Children and Teens:
- Growth and Development: As children grow, their body fat percentage changes, and growth patterns differ between boys and girls.
- Puberty: Hormonal changes during puberty can affect weight and body composition.
Summary:
- Calculation: BMI is calculated the same way for all ages.
- Interpretation: For adults, age doesn’t affect BMI categories. For children and teens, age and sex are crucial for interpreting BMI accurately.
If you’re concerned about your BMI or how it relates to your age, it’s best to consult a healthcare professional who can provide personalized advice.