BMI (or Body Mass Index) is a measure used by the NHS to assess if an individual is underweight (<18,9 BMI), healthy weight (19 to 24,9), overweight (25 to 29,9), obese (29,9 to 39,9) or morbidly obese (>40). BMI is calculated by dividing a person’s weight (in kg) by their height (in cm). This index is not considered very accurate as it doesn’t consider the body percentage of fat vs lean muscle (the latter of which is more dense and can weigh more).