Body Mass Index (BMI) Calculator

Body Mass Index (BMI) is an international standard established by the World Health Organization (WHO) to classify adult nutritional status and screen for potential health risks associated with underweight, overweight, and obesity. Although simple to calculate, understanding what BMI indicates—and where its diagnostic limitations lie—is critical for realistic wellness tracking.

The standard WHO categories define a BMI between 18.5 and 24.9 as normal or healthy weight. A BMI below 18.5 indicates underweight, which may signal nutritional deficiency or underlying metabolic conditions. Scores from 25.0 to 29.9 fall into the overweight category, while values of 30.0 and above indicate obesity, subdivided into Class I, Class II, and Class III categories.

It is important to remember that BMI is a surrogate measure of body composition. Athletes with high muscle mass frequently register as "overweight" because dense muscle tissue weighs more than fat tissue. Conversely, elderly individuals with lower muscle mass can register a "normal" BMI despite elevated visceral fat. Medical practitioners routinely combine BMI with waist circumference and body fat percentage for comprehensive evaluation.