When MRP runs, it compares each item’s demand with existing supply orders for each period. It automatically reschedules planned orders to reflect changes in the plan and generates an action message for each rescheduled order. Some orders MRP cannot change because they are firm planned or within the time fence specified in the item planning data. For these, it generates action messages suggesting that these orders be rescheduled to balance supply with demand.

When MRP reschedules planned orders for higher-level end items, lower-level components dependent on the rescheduled demand remain associated with the original supply order date. They are not automatically rescheduled based on where action messages say parent orders should be moved. To adjust for this: