Your ideal weight depends on your age, height, build and how much weight you carry. Calculating your body mass index (BMI) will give you an indication of where you stand in the healthy weight range. The BMI is a calculation of your weight in relation to your height. This calculation can be used by adults between the ages of 20 and 65 years. It is not a reliable test for children, women who are pregnant or breastfeeding, or serious / professional sports people. Your doctor can better assess your weight in relation to height in these circumstances.