Determine a user's timezone

Question

Is there a standard way for a web server to be able to determine a user\'s timezone within a web page?

Perhaps from an HTTP header or part of the user-agent

Answer 1

Getting a valid TZ Database timezone name in PHP is a two-step process:

1. With JavaScript, get timezone offset in minutes through getTimezoneOffset. This offset will be positive if the local timezone is behind UTC and negative if it is ahead. So you must add an opposite sign to the offset.

   var timezone_offset_minutes = new Date().getTimezoneOffset();
   timezone_offset_minutes = timezone_offset_minutes == 0 ? 0 : -timezone_offset_minutes;
   

   Pass this offset to PHP.

2. In PHP convert this offset into a valid timezone name with timezone_name_from_abbr function.

   // Just an example.
   $timezone_offset_minutes = -360;  // $_GET['timezone_offset_minutes']
   
   // Convert minutes to seconds
   $timezone_name = timezone_name_from_abbr("", $timezone_offset_minutes*60, false);
   
   // America/Chicago
   echo $timezone_name;

I've written a blog post on it: How to Detect User Timezone in PHP. It also contains a demo.