Method returns a string containing the number of days since a given reference date

Days since Reference Date

- (NSString *)daysSinceDate:(NSDate *)referenceDate
{
    NSDate *today = [NSDate date];
	NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
	NSCalendarUnit units = NSYearCalendarUnit | NSMonthCalendarUnit | NSWeekCalendarUnit | NSWeekdayCalendarUnit | NSDayCalendarUnit;
	
	NSDateComponents *components = [gregorian components:units fromDate:referenceDate toDate:today options:0];
	NSInteger days = [components day];
    NSInteger years = [components year];

    for (NSInteger j = 0; j < years; j++) {
        components.year = j;
        NSDate *newDate = [gregorian dateByAddingComponents:components toDate:referenceDate options:0];
        NSRange rangeDays = [gregorian rangeOfUnit:NSMonthCalendarUnit
                                            inUnit:NSYearCalendarUnit
                                           forDate:newDate];

        for (NSInteger i = 0; i < rangeDays.length; i++) {
            components.month = i;
            NSDate *newMonth = [gregorian dateByAddingComponents:components toDate:referenceDate options:0];
            NSRange rangeYears = [gregorian rangeOfUnit:NSDayCalendarUnit
                                                inUnit:NSMonthCalendarUnit
                                               forDate:newMonth];
            days += rangeYears.length;
        }
    }
    return days;
}