1.  Create new Reminders.
2.  On the General tab, Select:
-Reminder type: Create custom data file, Per Pledge
-Date: specific range (go as far back as possible to include all pledges ie. 1/1/1990-today)
-Run Date: the day you want to look for past due pledges as of x day
 
3. Click Export.
4. Name and Save the file.
5. The Total Due column will be the column that equals the Past Due Total.

NOTE: This data will only be accessible in a format outside of Raisers Edge (ie. Excel, Word).