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For manufacturing workstations, there is a trade-o ff between throughput and meeting product due dates.Models for predicting flow time distributions are helpful in this respect. A model of a workstation typically has to include the process time distributions of the machines in the workstation, the dispatching rule, and other disturbances that aff ect the flow time performance. A detailed simulation model may be used to predict the flow time distributions of a workstation. However, such a model typically involves considerable development time, and obtaining all model parameters may be difficult. In this paper we propose a single-server aggregate model with a workload-dependent aggregate process time distribution, and a workload-dependent overtakingdistribution. The model involves little development time. The process time and overtaking ditribution in the aggregate model are determined from lot arrival and departure events measured at the considered workstation. Two simulation test cases are included to demonstrate the proposed method.