Hi Dan,
Currently our Terms do not actually have any "calculation" that can do anything like that. It is only a text field and does not capture a number. I will add your request our "wish list". I cannot make any promises to if it will or won't get done, but we have noted your request. The other wrinkle with Terms is that then people would also want it to do "finance charges" for things that are overdue, so that adds a lot more complexity to this. Thanks for taking the time to write us!!!