NSDate *date = babyKicksAppDelegate.settings.LastMenstrual;
NSCalendar *gregorian = [[NSCalendar alloc]
initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents* dc1 = [[[NSDateComponents alloc] init] autorelease];
[dc1 setDay:280];
NSDate *tmpDate = [gregorian dateByAddingComponents:dc1 toDate:date options:0];
self.dueDateLabel.text = [outputFormatter stringFromDate:tmpDate];
我这个是增加天数的,你可以看看用法,应该差不多的。