Abstract: A method of updating a supply plan used to process customer requests in an available-to-promise (ATP) system. In one embodiment the method comprises updating a model of a supply chain process for one or more products sold by the ATP system and copying a current supply plan used by the ATP system to process customer requests to create a second supply plan. Thereafter, a first plurality of customer requests is received and orders from the requests are processed by the ATP system against the current supply plan while running the updated model of the supply chain process with the second supply plan as part of a process that creates a new supply plan. After the new supply plan is created, the new supply plan is synchronized with the old supply plan by synchronizing orders from the first plurality of customer requests scheduled against the old supply plan into the new plan while order promising continues against the old plan.