Due date calculation in SQ01/SQ02

Hi all,

I've created a query in SQ01 for customer open items and i'm trying to add a due date field. I've created some local fields, eg if payment terms are 7 days then add 7 days on to the baseline date.

There is one payment term I'm struggling with, this is ZC14 which means that the invoice is due for payment on the 14th day of the following month. Does anyone know any ABAP code that could be used to calculate this in a custom field in SQ02?

Thank you in advance.

Kind regards

Dave