This question is almost impossible to answer. How can you calculate the effects of exercising? It is absolutely impossible! Different people have different metabolic rates and they all consume different calories of food. The time taken for you to lose belly fat will directly be dependent on the size of your belly (for starters) and on the intensity with which you exercise. It will also depend on your daily diet, and the amount of calories you consume every day. All you can do is chalk up a good diet, stick to it like your life depends on it, and exercise.