Sit-to-stand (STS) is a common activity in daily lives which requires relatively high joint torques and a robust coordination of lower and upper extremities with postural stability. Many elderly, people with lower limb injuries, and patients with neurological disorders or musculoskeletal abnormalities have difficulties in accomplishing this task. In contrast to the literature on numerous experimental studies of STS, there are limited studies that were carried out through simulations. In literature, mostly bilateral symmetry was assumed for STS tasks, however even for healthy people, it is more difficult to perform STS tasks with a perfect bilateral symmetry. The goal of this research is to develop a threedimensional unassisted STS motion prediction formulation for healthy young individuals. Predicted results will be compared with experimental results found in literature for the validation of the proposed formulation.