BMI is weight in kilograms divided by height in metres squared. A BMI of 18.5 to 24.9 is the healthy range, below 18.5 is underweight, 25 to 29.9 is overweight and 30 or above is obese. For example, 70 kg at 170 cm gives a BMI of 24.2.
BMI is a screening tool, not a diagnosis. It does not measure muscle or body fat, so speak to a doctor about your health.
BMI is a quick starting point for tracking weight over time. It does not separate muscle from fat, so athletes and older adults should treat it with care. For lifestyle advice, see our health tips page.