int daysToAdd = 1;
NSDateComponents *components = [[[NSDateComponents alloc] init] autorelease];
[components setDay:daysToAdd];
// create a calendar
NSCalendar *gregorian = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];
NSDate *newDate = [gregorian dateByAddingComponents:components toDate:datePicker.date options:0];