A Body Mass Index (BMI) calculator determines body fat by dividing weight (in kilograms) by the square of height (in meters) or using imperial units with a conversion factor. It categorizes results into underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), or obese (≥30) based on who standards. for underweight individuals, it suggests increasing calorie intake with nutrient-rich foods and consulting a dietitian. those in the range are encouraged to maintain balanced diet regular exercise. users receive recommendations gradual weight loss through healthy eating, portion control, activities like walking swimming.