This site calculates your Basal Metabolic Rate. Your BMR is the energy in Calories you burn in a day when doing nothing else. Working, exercize, and other normal daily activities are added to this value.
Remember that it takes 3,500 calories to burn off a pound of fat. Take your BMR add your workout and that is about how much you burn a day. Say you want to lose 1 lb a week you need to burn 500 more calories a day then you would normally burn.