- mktime: documentation ( source)
- explode: documentation ( source)
- date: documentation ( source)
<?php
$checknew = explode("-", "20-11-2015");
$monthnow = $checknew[1];
$daynow = $checknew[0];
$yearnow = $checknew[2];
$rangenow = mktime(0, 0, 0, $monthnow, $daynow, $yearnow);
$datediff = date("Y-m-d",$rangenow) - date("Y-m-d");
echo $datediff;