that depends on the individual, for myself i eat clean pretty much year round and never really indulging. once every blue moon, i may have something. if your dieting, most common is once a week. If you can suceed one week, more power to you. people insist that metabolism would be slowed after sustained calorie reduced diet, which is true, but no need to cheat if you continually see results. once you reach a plateau, then i would add a cheat meal into the diet or increase calories.