Simply enter you current weight, your goal weight and the time in which you wish to achieve the weight loss and click calculate.
This calculator assumes that all your weight loss is fat loss. Alas, during weight loss people often lose water weight (especially if crash dieting), muscle mass and fat. However, if you are following the above guidelines and exercising (cardio and weights), you are probably losing mostly fat and gaining muscle (this will speed up metabolism). In this case, the calculator may underestimate your fat loss because you have added muscle weight. This is why scales are an unreliable tool in measuring your fat loss progress.