In the scheduling literature, estimation of job flowtimes has always been an important issue since the late sixties. The previous studies focus on the problem in the context of due date assignment and develop methods using aggregate information in the estimation process. In this study, we propose a new method which utilizes the job, shop and route information on an operational basis. The performance of the proposed method is measured using a simulation model. It is also compared with the existing methods for a wide variety of performance measures under various experimental conditions.