Gains will differ from one individual to another depending on body size and level of experience in the gym. To make sure you're gaining muscle, not fat, don't just consider your scale weight. Instead, rely on what you see in the mirror and use a tape measure twice a month to keep track of your waist and hips (you don't want to gain there) as well as your biceps, chest and quads. Also, don't think that you have to gain a set amount of weight each and every week. "Your mass gain doesn't have to be uniform," Aceto explains. That means you can gain 1/2 pound one week and 1 1/2 the next, perhaps none the third week and still remain on course. "Expecting uniform gains ignores the intricate makeup of the body and the way it gains mass - or loses fat - which is by no means in linear fashion," adds Aceto.