Calculate if DST active for a given timestamp and offset

Question

Given a unix timestamp and timezone offset relative to UTC (e.g. -5), is it possible to calculate if DST is active?

I can do something like:

<?php
  echo 'DST enabled? ' . date('I', 1345731453) ."<br>"; 
?>

But I cannot see how to pass in an offset or a TimeZone.

Im guessing also that there is a difference between the timezone and the offset, given that specific countries support DST?

Appreciate any thoughts.

Yes indeed, a UTC offset doesn't say anything about which country it is, which means you cannot really determine the DST setting. — deceze, Aug 23 '12 at 14:55
Thanks, I think I have found my solution - http://stackoverflow.com/questions/1586552/how-to-tell-if-a-timezone-observes-daylight-saving-at-any-time-of-the-year — Ben, Aug 23 '12 at 15:02

score 1 · Accepted Answer · answered Aug 23 '12 at 15:06

1

Correct, you need to start with date and tz to determine offset.

in 5.3+ you can get transitions for start/end period, so you can just use your timestamp for both, something like this:

$inputTime = $your_unix_timestamp;
$inputTZ = new DateTimeZone('Europe/London'); 

$transitions = $inputTZ->getTransitions($inputTime,$inputTime); 
$offset = $transitions[0]['offset'];

$offset is the DST offset at the time in question

answered Aug 23 '12 at 15:06

Colin Pickard

45,724
13
98
148

Small warning: in your example $offset will hold the complete offset towards GMT+0, not just the amount that DST adds to it. So in this case it works, because you're using London as your timezone. But if you were to use Athens (GMT+3 in the summer), $offset would 10800 (3 hours), not 3600 (the 1 hour DST offset) I'm still working on this myself, but I think the best way to see if DST is *active*, is using DateTime's format('I'). – Dieter Apr 24 '13 at 16:32
Thanx this simplified some thing for me. – Esocoder Aug 27 '18 at 00:13

score 0 · Answer 2 · answered Aug 23 '12 at 15:05

Get the timezone with:

$old_zone = ini_get('date.timezone');

Change it to the one you want:

ini_set('date.timezone', 'Europe/Brussels');

Revert back:

ini_set('date.timezone', $old_zone);

The PHP timestamp is always UTC. Depending on your timezone setting it determine what time to show.

Calculate if DST active for a given timestamp and offset

2 Answers2