- time: documentation ( source)
- floor: documentation ( source)
- strtotime: documentation ( source)
<?php
$to_date = time("2014-01-02"); // Input your date here e.g. strtotime("2014-01-02")
$from_date = strtotime("2012-01-31");
$day_diff = $to_date - $from_date;
echo floor($day_diff/(60*60*24));
?>