compute the date two weeks ago from today,

  NSDate *today = [NSDate date];
    NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *offsetComponents = [[NSDateComponents alloc] init];
    [offsetComponents setDay:-14];  // 14 days back from today
    self.twoWeeksAgo = [gregorian dateByAddingComponents:offsetComponents toDate:today options:0];
    [offsetComponents release];
    [gregorian release];