Hi Jeetendar,
Not sure I understand your question: In payment terms configuration (OBB8), you can specify that the posting date should be used as baseline date. Alternative being document date, entry date or manually set date.
Purchase orders have no posting date so the system use the expected delivery date as baseline date. For goods and invoices receives, the system use the posting date as baseline date if configured as such in the payment term.
Hope it is clear, if not please clarify your request.
Regards
Th.