Body Mass Index (BMI) is calculated by dividing an individual's weight in kilograms by their height in meters squared (kg/m²). This index serves as a preliminary screening tool for categorizing individuals into weight categories: underweight, normal weight, overweight, and obese. While BMI provides a quick assessment of potential health risks associated with body weight, it does not account for muscle mass or body composition, making it important to consider additional measurements for a comprehensive view of health.