GMT to Local & Local to GMT

To convert from a localDate to GMT:

-(NSString *)localToGMT{
  
    NSDate *currDate = [NSDate date];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    NSString *dateString = [dateFormatter stringFromDate:currDate];
   
    NSDate *localDate = [dateFormatter dateFromString:dateString];
    NSTimeInterval timeZoneOffset = [[NSTimeZone systemTimeZone] secondsFromGMTForDate:localDate];
    NSDate *gmtDate = [localDate dateByAddingTimeInterval:-timeZoneOffset]; // NOTE the "-" sign!
    NSString *gmtdateString = [dateFormatter stringFromDate:gmtDate];
   
    [dateFormatter release];
    return gmtdateString;
}
To convert from a GMT date to a localDate:

-(NSString *)GMTToLocal:(NSString *)GMTdateString{
   
    NSDateFormatter *format = [[NSDateFormatter alloc] init];
    [format setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
   
    NSDate *gmtDate  = [format dateFromString:GMTdateString];   
   
    NSTimeInterval timeZoneOffset = [[NSTimeZone systemTimeZone] secondsFromGMTForDate:gmtDate];
    NSDate *localDate = [gmtDate dateByAddingTimeInterval:timeZoneOffset];
    [format setDateFormat:@"hh:mm:ss a, yyyy-MM-dd "];
    NSString *localDateString = [format stringFromDate:localDate];
   
    [format release];
    return localDateString;
}

Help Link : 

http://stackoverflow.com/questions/1862905/nsdate-convert-date-to-gmt/1863042#1863042