Questions Days Past Due

I am trying to write I GI that will feed a business event to take certain sales orders off hold.  One of the criteria I need to evaluate is the customers current Days Past Due.  I see where the Days Past Due limit is set on the Customer but I don't see anywhere that the current past due days is stored in a table.

Any ideas?

Or do I have to calculate it on the fly from the oldest open invoice due date? (Which will be problematic in the GI since I will need to avoid grouping - because of the Business Event)