DATEDIF is a hidden function in Excel. http://www.exceltrick.com/formulas_macros/excel-datedif-function/
use (to diff excluding weekend) :
1
2
//http://www.mrexcel.com/forum/excel-questions/335055-datedif-excluding-weekends.html
=NETWORKDAYS(A1,B1)
#excel
origin - http://www.pipiscrew.com/?p=5952 excel-datedif-and-networkdays