Goods Receipt PO due date cannot auto change

Dear All,

Would like to ask about a question that the Due Date in the Goods Recepit PO won't aunto changed to the date that plus the credit terms day.

for example i open this po today (18.09.2008) for BP-A which has a credit terms day as 30 days. but the Due Date will not auto change to 18.10.2008, is there any setting can set about it ?

Please kindly help one this. thank you very much