How to compare two dates in php

The date_diff() function returns the difference between two DateTime objects.

If the first date is before the second date a positive number of days will be returned; otherwise a negative number of days:

<?php
$date1=date_create("2013-03-15");
$date2=date_create("2013-12-12");
$diff=date_diff($date1,$date2);
echo $diff->format("%R%a days");
?>

output will be "+272 days" ;

changing $date1 = "2014-03-15"

 <?php
    $date1=date_create("2014-03-15");
    $date2=date_create("2013-12-12");
    $diff=date_diff($date1,$date2);
    echo $diff->format("%R%a days");
    ?>

Output will be "-93 days"

Using DateTime::createFromFormat:

$format = "d_m_y";
$date1  = \DateTime::createFromFormat($format, "03_01_12");
$date2  = \DateTime::createFromFormat($format, "31_12_11");

var_dump($date1 > $date2);

You will have to make sure that your dates are valid date objects.

Try this:

$date1=date('d/m/y');
$tempArr=explode('_', '31_12_11');
$date2 = date("d/m/y", mktime(0, 0, 0, $tempArr[1], $tempArr[0], $tempArr[2]));

You can then perform the strtotime() method to get the difference.

Not answering the OPs actual problem, but answering just the title. Since this is the top result for "comparing dates in php".

Pretty simple to use Datetime Objects (php >= 5.3.0) and Compare them directly

$date1 = new DateTime("2009-10-11");
$date2 = new DateTime("tomorrow"); // Can use date/string just like strtotime.
var_dump($date1 < $date2);