BUSDAYDIFF

BUSDAYDIFF()
Returns the number of business days between two dates.

REMARKS
* You can use the built-in NETWORKDAYS.INTL function to return the number of working days between two dates excluding weekends and holidays.
* You can use the user defined BUSDAYNEXT function to
* You can use the user defined BUSDAYPREVIOUS function to
* You can use the user defined BUSDAYMONTHSTART function to
* You can use the user defined BUSDAYMONTHEND function to
* You can use the user defined BUSDAYYEARSTART function to
* You can use the user defined BUSDAYYEAREND function to
* You can use the user defined BUSDAYSADD function to
* You can use the user defined BUSDAYNTH function to

Public Function BUSDAYDIFF( _ 
         ByVal dtDateStart As Date, _ 
         ByVal dtDateEnd As Date) _ 
         As Date 

   BUSDAYDIFF = Application.WorksheetFunction.NetworkDays(dtDateStart, dtDateEnd) 
End Function 

For instructions on how to add this function to a workbook refer to the page under Inserting Functions