You can calculate your body mass index (BMI) by dividing your weight in kilograms (kg) by your height in meters squared (m²). This formula helps estimate body fat and is used by healthcare professionals to help determine whether you’re at a healthy or unhealthy weight.

For people ages 20 and older, BMI is broken down into the following categories:

CategoryWeight stage
underweightless than 18.5
healthy weight18.5 to less than 25
overweight25 to less than 30
obesity30 or greater

BMI is interpreted differently for children and teenagers to account for growth patterns. It’s measured using a chart based on your age and sex, which places you in a percentile range.

For people ages 2 to 19, BMI is broken down into the following percentiles:

CategoryPercentile
underweightbelow 5th
healthy weight5th to 85th
overweight85th to 95th
obese95th and above

It’s important to note that BMI has certain limitations and is not always an accurate way to measure health. It cannot differentiate between muscle mass and body fat and also fails to take into account how individual factors may affect your weight and height, such as your age, sex, and race.

Read more about the downsides of BMI as a predictor of health.

Medically reviewed by Alissa Palladino, MS, RDN, LD, CPT

Alissa Palladino is a registered dietitian and certified personal trainer based in Atlanta, Georgia. Since 2014, Alissa has worked in a variety of corporate, community, medical, and fitness settings with diverse audiences supporting a range of health conditions and goals. Her focus areas include sports nutrition, weight management, diabetes, high blood pressure/cholesterol, and cardiovascular disease.

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