Calculating the number of work days between two dates
When calculating the difference between two dates, you may want to exclude weekends and holidays.
For example, you may need to know how many business days fall in the period from beggining of June till September 17. This calculation should exclude Saturdays, Sundays, and holidays.
The NETWORKDAYS function calculates the difference between two dates, excluding weekend days (Saturdays and Sundays).
As an option, you can specify a range of cells that contain the dates of holidays, which are also excluded. Excel has absolutely no way of determining which days are holidays, so you must provide this information in a range.