How BMI is calculated
BMI is weight in kilograms divided by height in metres squared. WHO ranges: under 18.5 underweight, 18.5-24.9 normal, 25-29.9 overweight, 30+ obese.
Limits of BMI
BMI does not distinguish muscle from fat, so athletes can read as overweight while being lean, and it can understate body-fat risk in older adults. Treat it as a population screening number, not a diagnosis — waist measurement and a medical checkup tell you more.