Realistic Delivery Date in IWBK transaction

Hi,

How is the realistic delivery date in IWBK transaction calculated? What are the parameters considered?

Most of the entries shows the Realistic delivery date as today's date. When is the realistic delivery date taken as today's date?

A couple of observations

Even if planned delivery date is in the past, realistic date need not be today's date

Even if Goods Receipt processing time and Plnd Delivery Time is not entered in the PO, realistic date need not necessarily be today's date