I got the Information from Navision 2013 R2 Helpf, hope it will help you.
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Calculations
When Microsoft Dynamics NAV calculates the customer’s delivery date, it performs two tasks:
• Calculates the earliest delivery date when the customer has not requested a specific delivery date.
• Verifies if the delivery date requested by the customer or promised to the customer is realistic.
If the customer does not request a specific delivery date, the shipment date is set to equal the work date, and availability is then based on that date. If the item is in inventory, Microsoft Dynamics NAV calculates forward in time to determine when the order can be delivered. This is accomplished by the following formulas:
•Shipment Date + Outbound Warehouse + Planned Shipment + Handling Time = Date
•Planned Shipment Date + Shipping Time = Planned Delivery Date
Microsoft Dynamics NAV then verifies if the calculated delivery date is realistic by calculating backward in time to determine when the item must be available to meet the promised date. This is accomplished by the following formulas:
•Planned Delivery Date - Shipping Time = Planned Shipment Date
•Planned Shipment Date - Outbound Warehouse Handling = Shipment Date
The shipment date is used to make the availability check. If the item is available on this date, Microsoft Dynamics NAV confirms that the requested/promised delivery can be met by setting the planned delivery date to equal the requested/promised delivery date. If the item is unavailable, it returns a blank date and the order processor can then use the CTP functionality.
Based on new dates and times, all related dates are calculated according to the formulas listed earlier in this section. The CTP calculation takes longer but it gives an accurate date when the customer can expect to have the item delivered. The dates that are calculated from CTP are presented in the Planned Delivery Date and Earliest Shipment Date fields in the Order Promising Lines window.
The order processor finishes the CTP process by accepting the dates. This means that a planning line and a reservation entry are created for the item before the calculated dates to ensure that the order is fulfilled.
