- mktime: documentation ( source)
- floor: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$dt_inicio = date("Y-m-d", strtotime('14/10/2013'));
$dt_final = date("Y-m-d", strtotime('28/10/2013'));
$i = mktime(0,0,0,10,14,2013);
$f = mktime(0,0,0,10,28,2013);
print floor(($f - $i)/86400);
print '\n';
print floor(($dt_final - $dt_inicio)/86400);