Objective: To evaluate weight loss results in three surgical procedures and the importance of measuring “expected BMI”. Patients and Methods: We have evaluated 2006 patients who had undergone surgery with Roux-and-Y Gastric Bypass (RNYGB),vertical Gastrectomy (VG)and a Single Anastomosis Gastric Bypass (SAGB). Results: A statistical study has evaluated the final “expected” BMI after bariatric surgery and arrives to a prognosis formula. Conclusions: With statistical work surgical techniques may be proposed depending on the patient’s initial BMI.