Safety of simultaneous bilateral TKA (simBTKA) and staged BTKA (staBTKA) have been compared in previous systematic reviews but functional outcome remains neglected aspect of the debate. We performed a systematic review of contemporary literature to compare the functional outcome of simBTKA and staBTKA. We searched PubMed/MEDLINE, EMBASE and Cochrane Central Database to identify all articles published between 2000 and July 2020 that evaluated the outcome of patients undergoing BTKA either in simultaneous or staged manner. Ten articles were identified which met the inclusion criteria. Functional outcome was reported in terms of Knee Society score (KSS), range of motion (ROM), Oxford Knee Score (OKS) and Western Ontario and McMaster University score (WOMAC) in seven, five, four and two studies respectively. KSS gained on average 66.6 points (47.5-95.3) for simBTKA and 65.1 points (44.4-97.2) for staBTKA without significant difference between two groups. There was no difference in post-operative ROM (maximum post-operative flexion being 124.4 and 125.1 for simBTKA and staBTKA groups respectively). Mean improvement in OKS ranged from 20 to 32.6 for simBTKA and 21.6 to 33.1 for staBTKA. There was moderate evidence to suggest that both simultaneous BTKA and staged BTKA produce equivalent improvement in functional scores.