Change Invoice stage setup to allow calculated invoice due date:
     1.  Have all users sign out of Accounts Payable.
     2.  Verify you have a current backup of your division.
     3.  From Accounts Payable, select Setup, Master Records, Stages.
          a.  If you know the number of your Invoice stage, select C to C)hange and at the Stage prompt type the number of your Invoice stage.
          b.  If you do not know the number of your Invoice stage, select S to S)croll the list of your stages and then select C to C)hange.  At the Stage prompt type the number of your Invoice stage.
     4.  At Enter field to be changed, type 7.
     5.  Press Enter until you are at the Stage date field.
     6.  Press F1 and select C - Field is calculated.
     7.  Press Enter and F2.
     8.  Press Enter to accept.
     9.  Press Esc and select E to E)nd.

Maintain Vendor Net Days from the Discounts tab:
     1.  From Accounts Payable, click Open and click the Vendor folder.
     2.  Enter the number of days from the Invoice date that payment is due to the vendor in the Net Days on the Discounts tab of your Vendors.
     3.  Your Invoice stage Stage Date field has been changed to C - Calculated and the Due Date on the Obligation Header tab automatically calculates once the Invoice Date is entered.