How much weight a person who has weight loss surgery depends on multiple factors including the type of procedure chosen. On average, a patient who has a lap band procedure can expect to lose about 45% of excess body weight (i.e., 45% of the amount of weight over the patient’s ideal body weight.) With a sleeve gastrectomy, the average is about 60% excess body weight loss. With gastric bypass, the average excess body weight loss is about 65-70%.