Body Mass Index (BMI) is a calculation using a person's height and weight to estimate whether they are underweight, normal weight, overweight, or obese. The formula divides weight in kilograms by height in metres squared. While BMI is widely used as a screening tool, it has significant limitations—it does not distinguish between muscle and fat, account for bone density, or consider where fat is distributed on the body. Athletes may have high BMIs due to muscle mass, while others with 'normal' BMIs may carry unhealthy visceral fat. Health professionals increasingly use BMI alongside other measures rather than as a sole indicator of health.