Date difference in Weeks , days, Hrs

@interface NSDateFormatter (Extras)
+ (NSString *)dateDifferenceStringFromString:(NSString *)dateString
                                  withFormat:(NSString *)dateFormat;
@end
@implementation NSDateFormatter (Extras)
+ (NSString *)dateDifferenceStringFromString:(NSString *)dateString
                                  withFormat:(NSString *)dateFormat{
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  [dateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
  [dateFormatter setDateFormat:dateFormat];
  NSDate *date = [dateFormatter dateFromString:dateString];
  [dateFormatter release];
  NSDate *now = [NSDate date];
  double time = [date timeIntervalSinceDate:now];
  time *= -1;
  if(time < 1) {
    return dateString;
  } else if (time < 60) {
    return @"less than a minute ago";
  } else if (time < 3600) {
    int diff = round(time / 60);
    if (diff == 1) 
      return [NSString stringWithFormat:@"1 minute ago", diff];
    return [NSString stringWithFormat:@"%d minutes ago", diff];
  } else if (time < 86400) {
    int diff = round(time / 60 / 60);
    if (diff == 1)
      return [NSString stringWithFormat:@"1 hour ago", diff];
    return [NSString stringWithFormat:@"%d hours ago", diff];
  } else if (time < 604800) {
    int diff = round(time / 60 / 60 / 24);
    if (diff == 1) 
      return [NSString stringWithFormat:@"yesterday", diff];
    if (diff == 7) 
      return [NSString stringWithFormat:@"last week", diff];
    return[NSString stringWithFormat:@"%d days ago", diff];
  } else {
    int diff = round(time / 60 / 60 / 24 / 7);
    if (diff == 1)
      return [NSString stringWithFormat:@"last week", diff];
    return [NSString stringWithFormat:@"%d weeks ago", diff];
  }   }

@end

Help Link:

http://stackoverflow.com/questions/902950/iphone-convert-date-string-to-a-relative-time-stamp