The amount of weight that is healthy to lose is dependent on your BMI (Body Mass Index). I would say a person who is an average height between 5'6-6'0 but weighs an exceedingly amount should lose about 25-30 pounds, but a person who is the right on or a bit higher than there weight intended for there height should lose a healthy 8-10 pounds. When a slimmer person is working out they gain muscle weight but an over weight persons body does not work on building muscle first it works on burning fat then building muscle when at a healthy weight. So to recap a healthy weight loss for an average person is 8-10 pounds and for a heavier person 25-30
Hope I helped a bunch :)