Many doctors and health websites recommend that you determine your BMI with an online BMI calculator, and make sure you are within the healthy ranges. BMI stands for body mass index, and can help you see where you stand. Enter your gender, weight and height, and you will receive a numeric score. Under 18.5 means underweight, 18.5-25 means healthy, 25-30 means overweight, and 30 or higher means obese. Talk to your doctor if you find yourself in the obese or underweight category, as there may be health risks involved.