Hi, i m Dr.Fatima ,working as an Assistant Doctor at Alsa Pakistan.BMI is an effective way to estimate the amount of extra weight on the body that could lead to various health problems. With increasing BMI, the body size increases leading to higher risks of obesity-related health conditions such as joint pains, breathing difficulties, metabolic conditions such as diabetes, high blood pressure, high cholesterol, high uric acid, and even infertility.So a BMI calculator tell you whether your current weight is healthy or not.