Why is the local timestamp equal to the UTC timestamp?

Question

If date() formats a local time/date, and gmdate() formats a GMT/UTC date/time, why is this true?

date_default_timezone_set('America/Los_Angeles');
var_dump(date('U') === gmdate('U')); // true

On the command line:

$ php -r "date_default_timezone_set('America/Los_Angeles'); var_dump(date('U') === gmdate('U'));"
bool(true)

Why is the local timestamp equal to the UTC timestamp for different time zones?

Timestamps are always in UTC. Formatted dates are localized according to the timezone setting. — mario, Mar 22 '13 at 01:59

John Conde · Accepted Answer · 2013-03-22T02:04:23.007

4

Because timestamps are seconds since the Unix Epoch (January 1 1970 00:00:00 GMT). Notice the GMT? No matter what time zone you're in, the timestamp is relative to that time and timezone.

What you really want to do is:

$local = new DateTime();
$local->setTimeZone(new DateTimeZone('America/Los_Angeles'));
$gmt   = new DateTime();
$gmt->setTimeZone(new DateTimeZone('UTC'));
var_dump($local === $gmt);

edited Mar 22 '13 at 02:04

answered Mar 22 '13 at 01:59

John Conde

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Did you mean $gmt->setTimeZone(new DateTimeZone('UTC')); ? – SoTes Mar 22 '13 at 02:06
Yes. Thank you for catching that. – John Conde Mar 22 '13 at 02:08
Thanks for the help! Makes sense why there's no `gmtime()` – SoTes Mar 22 '13 at 05:09

Why is the local timestamp equal to the UTC timestamp?

1 Answers1