The BMI calculator is just an rough estimation of your health. It measure the relation between length and bodyweight. A thin person with thin legs can live unhealthy and have a big belly. If he or she has a normal BMI it doesn’t mean he or she is healthy. A person with high BMI can have a perfect health.
Some thoughts about BMI
BMI is not only depending on how and what you eat or if you are fat or not. Your body constitution, illnesses and how much you train are all factors that affect the relation between length and weight. In some cases the BMI can be very misleadeading. A body builder can have extremely (dangerously) low body fat percentage but weight much more than the average person with the same height.
The BMI could indicate obesity without knowing how little fat and how much muscles that person have. If you, only based on the BMI, ordinates that person to eat less, his life could be in danger. The right ordination in that case could be the opposite, to eat more! Therefore, be careful when using the BMI and use it for what it is, a relation between a persons weight and height.