Traditionally, obesity has been defined as a weight at least 20% above ideal weight. More recent guidelines call for classifying obesity by using the body mass index (BMI). BMI is calculated based on your height and weight. However, BMI may classify as obese some people who aren't overweight but who are heavily muscled or big-boned. It also doesn't take into account the person's age. Waist-to-hip ratios (WHR) may be a better indication of disease risk, because they indicate if you have a lot of dangerous visceral fat inside your abdomen. Some doctors feel it's possible to be classified as obese and still be physically fit.