Calculate Days Between Dates, Ignoring Certain Weekdays

Question

I am developing a scheduling application, and part of it are events that repeat, say, daily in a given schedule. This schedule is only 'active' on certain days—think of it like a work week, where Saturdays and Sundays nothing happens.

I'd like to calculate the number of consecutive days between two dates, excluding those certain weekdays. I have a method that uses NSCalendar to do this, ignoring the excluded days, but did not see any methods on it (or related classes) that'd allow me to ignore certain days.

+ (NSInteger) OKDaysBetweenDate:(nonnull NSDate *) fromDateTime
                        andDate:(nonnull NSDate *) toDateTime {
    NSDate *fromDate;
    NSDate *toDate;

    NSCalendar *calendar = [NSCalendar currentCalendar];

    [calendar rangeOfUnit:NSCalendarUnitDay startDate:&fromDate
                 interval:NULL forDate:fromDateTime];
    [calendar rangeOfUnit:NSCalendarUnitDay startDate:&toDate
                 interval:NULL forDate:toDateTime];

    NSDateComponents *difference = [calendar components:NSCalendarUnitDay
                                               fromDate:fromDate toDate:toDate options:0];

    return [difference day];
}

A possibility I have thought of is checking how many weeks are between the two dates, multiplying that by the number of excluded days a week, and subtracting it from the end result, but that doesn't seem particularly clean to me.

Is there a better, more Cocoa-y (perhaps using NSCalendar or friends) way of implementing this?

Thanks.