Once, the number of batches, batch sizes, and production paths have been determined, and the tasks performed in the units have been sequenced, the determination of completion times is the last step in the scheduling of operations. In this paper, we deal with this problem considering that non permutation schedules may occur in multipurpose batch plants, once the task sequence in the units and the set-up, load, operation, unload and clean-up times are given. Finite wait (FW) interstage policy is assumed, meaning that intermediates may wait temporarily in discontinuous units if the waiting time does not exceed the maximum stability time for the intermediate, and assuming that no intermediate storage is available. A recursive procedure is presented to determine the start times and the duration of the possible waiting times in the discontinuous units. Then completion times are calculated adding the subtasks duration to the start times.