BMI Calculator

How BMI is calculated

Body Mass Index (BMI) is calculated by dividing your weight in kilograms by your height in meters squared. The formula is: BMI = weight (kg) / height (m)². Developed in the early 19th century by Adolphe Quetelet, BMI was adopted by the World Health Organization as a standard population-level screening tool for weight classification. It provides a quick, accessible way to assess whether your weight falls within a range associated with lower health risks. However, BMI has well-documented limitations. It does not distinguish between fat mass and lean mass, meaning muscular individuals may be classified as overweight despite having low body fat. It also does not account for bone density, age-related muscle loss, or differences in fat distribution. The National Institutes of Health recommend using BMI alongside other measurements such as waist circumference and body composition analysis for a more complete picture of health. BMI should be used as a starting point for conversation with your healthcare provider — not as a standalone diagnosis.

What your result means

According to the World Health Organization, a BMI between 18.5 and 24.9 is classified as normal weight and is associated with the lowest risk of weight-related health complications. A BMI below 18.5 indicates underweight, which can signal nutritional deficiencies or underlying medical conditions. A BMI between 25.0 and 29.9 falls in the overweight range, and a BMI of 30.0 or above is classified as obese — a category linked to increased risk of type 2 diabetes, cardiovascular disease, and certain cancers. It is important to understand that BMI does not tell the full story. A well-trained athlete may register a BMI above 25 due to muscle mass, while an older adult with a normal BMI may carry excess visceral fat. Ethnicity also plays a role — research from the NIH shows that health risks may begin at lower BMI thresholds in some populations. For a comprehensive assessment, discuss your result with a healthcare professional who can evaluate additional factors like body composition, blood pressure, and metabolic health.

Frequently Asked Questions