That would depend on your basal metabolic rate. Basically, that's the amount if calories your body burns just to 'run' it. But 500 calories is a dangerous amount to eat, so to maintain your weight, you should eat as many calories as you burn. If you eat, say, 500 calories a day, this puts your body into starvation mode, which causes the first thing you eat after entering it to be stored immediately as fat, which isn't good if you are trying to lose weight. Hope this helps!