The Material Requirements Planning (MRP) net requirement calculation determines material shortages by balancing total requirements against available supply. The basic formula is: Net Requirements = Gross Requirements - (Available Stock + Planned Receipts).

Both Production orders and firmed Planned orders are considered fixed receipt elements. They represent a committed supply of material that will be available on a specific date. MRP includes these quantities in the "Planned Receipts" portion of the calculation, thereby reducing the net requirement that needs to be covered by new procurement proposals.

C. Planned orders (unfirmed): Unfirmed planned orders are the result of a previous MRP run. During a new planning run, they are not treated as fixed receipts but are instead deleted and recreated based on the current situation.

D. ATP quantities: The Available-to-Promise (ATP) quantity is the output of a separate availability check, typically used in sales order processing. It is not a direct input element for the MRP net requirement calculation.

1. SAP S/4HANA Product Assistance, "Net Requirements Calculation": This official documentation details the elements used in the calculation. It explicitly lists "Production orders" and "Firmed planned orders" as fixed receipt elements that are taken into account. It also clarifies that unfirmed planned orders are deleted and replanned.

Source: SAP Help Portal, S/4HANA -> Enterprise Business Applications -> Manufacturing -> Production Planning and Control (PP) -> Material Requirements Planning (PP-MRP) -> MRP Planning Process -> Checks in the Planning Run -> Net Requirements Calculation.

2. SAP S/4HANA Product Assistance, "Planning Process": This section outlines the MRP run steps, stating that the system first calculates net requirements and then, in a second step, creates procurement proposals (like unfirmed planned orders) to cover these requirements. This confirms that unfirmed planned orders are an output, not an input to the calculation.

Source: SAP Help Portal, S/4HANA -> Enterprise Business Applications -> Manufacturing -> Production Planning and Control (PP) -> Material Requirements Planning (PP-MRP) -> MRP Planning Process.