Get remaining days in date range
Using System.Linq library the method can be rewritten like this:

public static int GetRemainingDays(DateTime startDate, DateTime endDate, ISet&lt;DayOfWeek&gt; includedDays)
{
    return Enumerable.Range(0, Int32.MaxValue)
        .Select(n =&gt; startDate.AddDays(n+1))
        .TakeWhile(date =&gt; date &lt;= endDate)
        .Count(date =&gt; includedDays.Contains(date.DayOfWeek));
}


Which can then be more easily called like this:

GetRemainingDays(startDate, endDate, 
    new HashSet&lt;DayOfWeek&gt;{DayOfWeek.Wednesday, DayOfWeek.Friday});


Note: You should test this (and the original version) against off-by-one errors.