Doug Steele posted this example for two dates.
SQL Statement:
'Number of weekdays between two dates, by Doug Steele MVP
SELECT DateDiff("d", dte1, dte2) -
DateDiff("ww", dte1, dte2, 1) * 2 -
IIf(Weekday(dte2, 1) = 7,
IIf(Weekday(dte1, 1) = 7, 0, 1),
IIf(Weekday(dte1, 1) = 7, -1, 0)) As WeekdaysBetween2Dates
FROM tblMyTable
That doesn't account for days that are holidays.
Hope this gets you started.