How do you calculate days overdue for an unpaid invoice?

Question

Sheet Reserve · Accepted Answer

For an invoice with an outstanding balance, subtract its due date from the review date and floor the result at zero. An invoice due October 1 and reviewed October 12 is 11 calendar days overdue. A future-due invoice shows zero, and a fully paid invoice shows zero in an open-balance report. Keep missing due dates explicit rather than treating them as old dates.

With due date C11, outstanding F11, and review date B7, a populated-date formula is =IF(F11<=0,0,MAX(0,$B$7-C11)).
How is payment lateness different from open overdue days?
For a paid invoice, historical lateness compares actual payment date with due date. The open-overdue measure describes what is still owed at review and should not be used as that historical measure.