BACKGROUND: Within a finite resource-limited national health service, a significant proportion of the cost of bariatric surgery is dependent on the length of stay of inpatients. This study was designed to investigate the factors that influence the length of post-operative stay in these patients. In particular, the effect of four common factors were explored in two bariatric procedures. METHODS: This is a retrospective study examining the length of stay in patients who underwent a laparoscopic sleeve gastrectomy (SG) and a laparoscopic Roux-En-Y gastric bypass (RNY) between July 2015 and February 2018 by a single surgeon. The significance of four factors were assessed: BMI, ASA grade, a diagnosis of diabetes and the day of the week the operation occurred. RESULTS: Median length of stay for SG patients was 2 [2,3] days. This was unaffected by our factors examined. Median length of stay for RNY was 2 [2,3] days. This was unaffected by ASA grade or a pre-existing diagnosis of diabetes. Day of the week and BMI significantly affected length of stay for RNY patients. Patients operated on a Friday stayed on average one day longer (p=0.002). Patients with a BMI over 60 stayed on average 2 days more (p=0.008) CONCLUSION: To optimise costs in the health service, more attention should be placed on when RNY and SG procedures are performed during the week. This is especially relevant when dealing with patients with high BMIs.