- abs: documentation ( source)
- floor: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$date = "2014-09-29";
$today = date();
$diff = abs(strtotime($date) - strtotime($today));
$days = floor(($diff - $years * 365*60*60*24 - $months*30*60*60*24)/ (60*60*24));
echo $days;