DayCount

DayCount[date1,date2] gives the number of days from date1 to date2.

DayCount[date1,date2,daytype] gives the number of days of the specified daytype from date1 to date2.

Examples

Count days between two dates:

DayCount[{2020, 1, 1}, {2020, 12, 31}]
(* 365 *)

Count only business days:

DayCount[{2020, 1, 1}, {2020, 1, 31}, "BusinessDay"]
(* 22 *)

Please visit the official Wolfram Language Reference for more details.