How do I get Greenwich Mean Time in PHP?

I would strongly suggest avoiding messing with UNIX timestamps to make it look like a different time zone. This is a lesson I've learnt the hard way, way too many times.

A timestamp is the number of seconds since Midnight 1 January 1970, GMT. It doesn't matter where you are in the world, a given timestamp represents the exact same moment in time, regardless of time zones. Yes, the timestamp "0" means 10am 1/1/70 in Australia, Midnight 1/1/70 in London and 5pm 31/12/69 in LA, but this doesn't mean you can simply add or subtract values and guarantee accuracy.

The golden example which stuffed me up every year for way too long was when daylight savings would crop up. Daylight savings means that there are "clock times" which don't exist in certain parts of the world. For example, in most parts of the US, there was no such time as 2:01am on April 2, 2006.

Enough quasi-intelligible ranting though. My advice is to store your dates in the database as timestamps, and then...

• If you need the local time at the server, use date()
• If you need to get GMT, then use gmdate()
• If you need to get a different timezone, use date_default_timezone_set() and then date()

For example,

$timestamp = time();

echo "BRISBANE: " . date('r', $timestamp) . "\n";
echo "     UTC: " . gmdate('r', $timestamp) . "\n";
date_default_timezone_set('Africa/Johannesburg');
echo "  JOBURG: " . date('r', $timestamp) . "\n";

// BRISBANE: Tue, 12 May 2009 18:28:20 +1000
//      UTC: Tue, 12 May 2009 08:28:20 +0000
//   JOBURG: Tue, 12 May 2009 10:28:20 +0200

This will keep your values clean (you don't have to be worrying about adding offsets, and then subtracting before saving), it will respect all Daylight Savings rules, and you also don't have to even look up the timezone of the place you want.

No matter in which GMT time zone the server is, here is an extremely easy way to get time and date for any time zone. This is done with the time() and gmdate() functions. The gmdate() function normally gives us GMT time, but by doing a trick with the time() function we can get GMT+N or GMT-N, meaning we can get the time for any GMT time zone.

For example, if you have to get the time for GMT+5, you can do it as follows

<?php 
  $offset=5*60*60; //converting 5 hours to seconds.
  $dateFormat="d-m-Y H:i";
  $timeNdate=gmdate($dateFormat, time()+$offset);
?>

Now if you have to get the time for GMT-5, you can just subtract the offset from the time() instead of adding to it, like in the following example where we are getting the time for GMT-4

<?php 
  $offset=4*60*60; //converting 4 hours to seconds.
  $dateFormat="d-m-Y H:i"; //set the date format
  $timeNdate=gmdate($dateFormat, time()-$offset); //get GMT date - 4
?>