PHP UTC to Local Time

Server Environment

Redhat Enterprise Linux
PHP 5.3.5

Problem

Let’s say I have a UTC date and time such as 2011-04-27 02:45 and I want to convert it to my local time, which is America/New_York.

Three questions:

1.) My code below might solve the problem, would you agree?

<?php

date_default_timezone_set('America/New_York');  // Set timezone.

$utc_ts = strtotime("2011-04-27 02:45");  // UTC Unix timestamp.

// Timezone offset in seconds. The offset for timezones west of UTC is always negative,
// and for those east of UTC is always positive.
$offset = date("Z");

$local_ts = $utc_ts + $offset;  // Local Unix timestamp. Add because $offset is negative.

$local_time = date("Y-m-d g:i A", $local_ts);  // Local time as yyyy-mm-dd h:m am/pm.

echo $local_time;  // 2011-04-26 10:45 PM

?>

2.) But, does the value of $offset automatically adjust for Daylight Savings Time (DST) ?
3.) If not, how should I tweak my code to automatically adjust for DST ?

Thank you 🙂

Answer

This will do what you want using PHPs native DateTime and DateTimeZone classes:

$utc_date = DateTime::createFromFormat(
                'Y-m-d G:i', 
                '2011-04-27 02:45', 
                new DateTimeZone('UTC')
);

$nyc_date = $utc_date;
$nyc_date->setTimeZone(new DateTimeZone('America/New_York'));

echo $nyc_date->format('Y-m-d g:i A'); // output: 2011-04-26 10:45 PM

See DateTime::createFromFormat man page for more information.

After some experimentation between time zones that do and do not currently have DST I have discovered that this will take DST into account. The same conversion using my method above renders the same resulting time.