The NETWORKDAYS function can do this ‑‑ it calculates the number of days between two dates ignoring Saturdays, Sundays and any holidays that you specify. You’ll find the function in the Excel Analysis ...

With or without holidays, you’ll need to use the networkdays function. And no, it has nothing to do with connectivity. The name means net workdays, not network days.

Excel 2003 users should note that the .xls file does not support the holiday formatting rule. It relies on the NETWORKDAYS () function, which was added to Excel 2007.