Question

How can I get the number of weekdays between two given dates without just iterating through the dates between and counting the weekdays?

Seems fairly straightforward but I can’t seem to find a conclusive correct answer that abides by the following:

1. The total should be inclusive, so GetNumberOfWeekdays(new DateTime(2009,11,30), new DateTime(2009,12,4)) should equal 5, that’s Monday to Friday.
2. Should allow for leap days
3. does NOT just iterate through all the dates between whilst counting the weekdays.

I’ve found a similar question with an answer that comes close but is not correct

Answer 1

From this link:

    public static int Weekdays(DateTime dtmStart, DateTime dtmEnd)
    {
        // This function includes the start and end date in the count if they fall on a weekday
        int dowStart = ((int)dtmStart.DayOfWeek == 0 ? 7 : (int)dtmStart.DayOfWeek);
        int dowEnd = ((int)dtmEnd.DayOfWeek == 0 ? 7 : (int)dtmEnd.DayOfWeek);
        TimeSpan tSpan = dtmEnd - dtmStart;
        if (dowStart <= dowEnd)
        {
            return (((tSpan.Days / 7) * 5) + Math.Max((Math.Min((dowEnd + 1), 6) - dowStart), 0));
        }
        return (((tSpan.Days / 7) * 5) + Math.Min((dowEnd + 6) - Math.Min(dowStart, 6), 5));
    }


  [1]: http://www.eggheadcafe.com/community/aspnet/2/44982/how-to-calculate-num-of-w.aspx

Tests (each test returns 5):

    int ndays = Weekdays(new DateTime(2009, 11, 30), new DateTime(2009, 12, 4));
    System.Console.WriteLine(ndays);

    // leap year test
    ndays = Weekdays(new DateTime(2000, 2,27), new DateTime(2000, 3, 5));
    System.Console.WriteLine(ndays);

    // non leap year test
    ndays = Weekdays(new DateTime(2007, 2, 25), new DateTime(2007, 3, 4));
    System.Console.WriteLine(ndays);