- var_dump: documentation ( source)
- floor: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$reg_date = '2014-05-25';
$expire = date('Y-m-d', strtotime($reg_date));
$diff = strtotime(date('Y-m-d')) - strtotime($expire);
$daysleft = floor( $diff / (60 * 60 * 24) );
var_dump($daysleft);