Is there a formula other than NOW or Today to Return the Date the Workbook was last Modified?

I have a relatively simple set of Workbooks that reference the worksheets within it and I don't want to have to manually go to the overview Worksheet every time and update the Current through or As of date.  These worksheets are involving some simple private loans and they calculate the interest on a monthly basis but are only updated about once a month.   I want the field (C3) in attached example to be the date of the last time that the Worksheet was Modified not the last time it was accessed.  Is there a simple formula to accomplish this?