Obesity is an increasingly common problem.Obesity is a term used to describe somebody who is very overweight and a lot of body fat. The risk factors or causes diseases that affect health. It can cause death. BMI is a measure of whether you're a healthy weight for your height. You can use the BMI healthy weight calculator to work out your score. a BMI of 25 to 29.9 means you are considered overweight. A BMI of 30 to 39.9 means you are considered obese.a BMI of 40 or above means you are considered severely obese.