- date_diff: documentation ( source)
- date_create: documentation ( source)
<?php
$datetime1 = date_create('13-11-2013');
$datetime2 = date_create('24-05-2013');
$interval = date_diff($datetime1, $datetime2);
echo $interval->format('%R%a dias');
echo '24-05-2013 (-143 dias)';