I'm trying to create an effective due date on a bill, for those bills we want to make sure to send out 1 week before the due date. I have a placeholder for the integer number of days prior to the due date that we want to pull the bill & pay it. How do I create a field on the bill which is {duedate}-{advancedaystopay} ? I'm trying to put it in the default value on the effective due date custom field...