MRP (Material Requirements Planning)

Material Requirements Planning (MRP) is the algorithm that compares demand (sales orders, forecasts, production component needs, transfer requirements) against supply (on-hand inventory, open purchase orders, planned production orders, transfer orders) and suggests the new purchase, production, and transfer orders needed to keep stock balanced through the planning horizon. In Business Central it runs through the planning worksheet; in Dynamics 365 Supply Chain Management it runs through Planning Optimization, the modern in-memory engine that replaced the legacy MRP. Output is a set of action messages — New, Increase, Decrease, Reschedule earlier, Reschedule later, Cancel — that planners review and accept.

In practice, MRP's output quality is entirely a function of the reordering policy and lead-time data behind each item, not the algorithm itself — the same engine that produces a perfectly reasonable purchase suggestion for one item can produce a nonsensical one for another simply because that item's safety stock, lot sizing rule, or vendor lead time was never set up correctly. This is why experienced planners start with simple policies (lot-for-lot for made items, a fixed reorder point for cheap purchased components) and add sophistication only where the added complexity earns its keep.

Where confusion shows up: MRP suggestions are just that — suggestions — and nothing changes in inventory or on order until a planner explicitly accepts an action message; a planning run that nobody reviews and accepts has no effect at all, which trips up new planners who expect the "planning worksheet" to place orders automatically. Planning Optimization in Dynamics 365 Supply Chain Management is architecturally a different engine from the legacy MRP it replaced (in-memory, faster, different tuning parameters) rather than the same algorithm with a new name, so guidance written for classic MRP doesn't always transfer directly to tuning Planning Optimization.