The measurement of weight loss after bariatric surgery is under constant review in order to obtain the ideal standard for reporting weight loss. Several formulas have been proposed for this purpose. Our goal is to analyse weight loss after sleeve gastrectomy, with or without antrum preservation through different measurement formulas. A prospective randomised study of 60 patients (30 patients with initial section at 3 cm from pylorus and 30 patients at 8 cm from the pylorus). We calculate the following variables at 3, 6 and 12 months from surgery: BMI, excess weight loss (%EWL), percentage of excess of BMI loss (%PEBMIL), expected BMI, % PEBMIL corrected by EBMI and percentage of total weight loss (%TWL). Weight evolution is similar in both groups, reaching a mean BMI of 33.62 +/- 4.35 and 34.48 +/- 4.23 kg/m(2) respectively 12 months after surgery, closer to expected BMI. TWL follows the same trend, with losses exceeding 30%, although 3 cm group is above the tables of percentiles made with our series. Regarding PEBMIL, the 3 cm group reaches 67.8% classified as excellent, while 8 cm group reaches 62.8% classified as a good result. EWL situates the best results for 3 cm group. Group 3 cm obtained a lower percentage of suboptimal results using EWL. %TWL places the 3 cm group in higher percentile than 8 cm group. Through EBMI, both groups are equally effective. It is necessary to have standardised dynamic tables for each surgical technique, becoming essential elements to measure weight loss after surgery.