The Significance of Planning Data for Negative Days and Positive Days in Microsoft Dynamics AX

One of the more confusing aspects of planning data within Microsoft Dynamics AX involves the significance of the policies for negative days and positive days.  The names of these two policies reflect the mathematics within the planning calculations, but the names do not readily convey their significance.  Understanding and correctly applying these policies directly impacts the generation of planned orders for an item, and the overall effectiveness of using Dynamics AX to model your business decisions. 

It is easier to view these policies as two fundamental assumptions related to the generation of planned orders.  The two assumptions can be labeled the rescheduling assumption and the fast-moving inventory assumption.  Each assumption has two options, where one option represents dominant business practices and the second option represents a special case. 

Rescheduling Assumption (Negative Days policy) The rescheduling assumption represents a key aspect of planning calculations in every ERP system.  In summary, it is typically easier to expedite an item's existing supply order (to meet demand within the item's lead time) rather than generating a new order.  A supply order can be a purchase order, transfer order or production order.  Stated another way, the planning calculations should generate an action message to expedite or "advance" an item's existing supply order to meet demand within the item's lead time, or generate a new planned order if that is not possible.  There are two basic options for the rescheduling assumption, as described below.

• Dominant Business Practice: Rescheduling Assumption based on Item Lead Time.   Most firms employ a companywide policy to indicate rescheduling assumptions should be based on each item's lead time.  The policy ...

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