How to detect user's timezone?

I need to know what time zone is currently my users are in based on their IP or http header.

I got many answer regarding this issue, but i could not understood those answer. Some said use -new Date().getTimezoneOffset()/60 (from here). But what does it mean?

I have a date_default_timezone_set("Asia/Calcutta"); in the root of my (index.php) page. So for this I have to get the timezone dynamically and set it in place of Asia/Calcutta.

Answers:

Answer

To summarize Matt Johnson's answer in terms of code:

<script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js">
</script>
<script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/jstimezonedetect/1.0.4/jstz.min.js">
</script>
<script type="text/javascript">
  $(document).ready(function(){
    var tz = jstz.determine(); // Determines the time zone of the browser client
    var timezone = tz.name(); //'Asia/Kolhata' for Indian Time.
    $.post("url-to-function-that-handles-time-zone", {tz: timezone}, function(data) {
       //Preocess the timezone in the controller function and get
       //the confirmation value here. On success, refresh the page.
     });
  });
</script>
Answer

Time zone information of the browser is not part of the HTTP spec, so you can't just get it from a header.

If you have location coordinates (from a mobile device GPS, for example), then you can find the time zone using one of these methods. However, geolocation by IP address is not a great solution because often the IP is that of an ISP or proxy server which may be in another time zone.

There are some strategies you can use to try to detect the time zone, such as using jsTimeZoneDetect library, which is a great starting point, but imperfect enough that you can't just rely on that alone. If you're using moment.js, there's a built in function in moment-timezone called moment.tz.guess() that does the same thing.

The idea of using JavaScript's getTimezoneOffset() function is flawed in that you are not getting a time zone - just a single offset for a particular date. See the TimeZone tag wiki's section titled "TimeZone != Offset".

However you look at it, ultimately you have to decide on one of two approaches:

OR

  • Only send time to the browser in UTC, and use JavaScript on the browser to convert to whatever local time zone the user might have their computer set to.

I discuss this in more detail (from a c# perspective) in this answer.

Answer

Dependencies:

  1. http://www.maxmind.com/download/geoip/api/php/php-latest.tar.gz
  2. http://geolite.maxmind.com/download/geoip/database/GeoLiteCity.dat.gz

    //Get remote IP
    $ip = $_SERVER['REMOTE_ADDR'];
    
    //Open GeoIP database and query our IP
    $gi = geoip_open("GeoLiteCity.dat", GEOIP_STANDARD);
    $record = geoip_record_by_addr($gi, $ip);
    
    //If we for some reason didnt find data about the IP, default to a preset location.
    if(!isset($record)) {
        $record = new geoiprecord();
        $record->latitude = 59.2;
        $record->longitude = 17.8167;
        $record->country_code = 'SE';
        $record->region = 26;
    }
    
    //Calculate the timezone and local time
    try {
        //Create timezone
        $user_timezone = new DateTimeZone(get_time_zone($record->country_code, ($record->region!='') ? $record->region : 0));
    
        //Create local time
        $user_localtime = new DateTime("now", $user_timezone);
        $user_timezone_offset = $user_localtime->getOffset();        
    }
    //Timezone and/or local time detection failed
    catch(Exception $e) {
        $user_timezone_offset = 7200;
        $user_localtime = new DateTime("now");
    }
    
    echo 'User local time: ' . $user_localtime->format('H:i:s') . '<br/>';
    echo 'Timezone GMT offset: ' . $user_timezone_offset . '<br/>';
    

citation: SGet visitor local time, sunrise and sunset time by IP with MaxMind GeoIP and PHP by Stanislav Khromov

Answer

This works fine...

  echo <<<EOE
   <script type="text/javascript">
     if (navigator.cookieEnabled)
       document.cookie = "tzo="+ (- new Date().getTimezoneOffset());
   </script>
EOE;
  if (!isset($_COOKIE['tzo'])) {
    echo <<<EOE
      <script type="text/javascript">
        if (navigator.cookieEnabled) document.reload();
        else alert("Cookies must be enabled!");
      </script>
EOE;
    die();
  }
  $ts = new DateTime('now', new DateTimeZone('GMT'));
  $ts->add(DateInterval::createFromDateString($_COOKIE['tzo'].' minutes'));
Answer

One solution is to ask them! Especially on members systems where you can capture/register a user - give them a choice at that point. Simple but accurate.

Answer

Timezone is not available in the HTTP header, but country (abbreviation) is in the ACCEPT_LANGUAGE header. It'll be something like "en-US" (US is the country code). This can be combined with the JavaScript information to get a good idea of the user's timezone.

This is what I'm using in JS:

function timezone() {
  var now = new Date();
  var jano = new Date(now.getFullYear(), 0, 1).getTimezoneOffset()/-60;
  var julo = new Date(now.getFullYear(), 6, 1).getTimezoneOffset()/-60;
  var tz = Math.min(jano, julo);
  if (jano != julo) tz += ((jano < julo) ? 'S' : 'W') + Math.abs(jano - julo);
  return tz;
}

This returns a string like "-6S1" for the central zone (standard time offset of -6 hours, DST active in the summer and adds 1 hour). I use a cookie to make this available to PHP. PHP searches the TZ database for zones that match this, and the country. For here (US, -6S1) there are 7 matching zones, the first is "America/Chicago".

BTW, there are 2 zones in the database where DST adds something other than 1 hour: Lord Howe Island (10.5W0.5) and Troll Station, Antarctica (0W2).

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