I recently needed a way to figure out the difference, in days, between two dates. Here is how I did it.

Using PHP:

$expireDate = "2006-02-07";

$year = substr($expireDate, 0, 4);
$month = substr($expireDate, 5, 2);
$day = substr($expireDate, 8, 2);

$splitExpireDate = (mktime(0, 0, 0, $month, $day, $year));
$today = (mktime(0, 0, 0, date("m"), date("d"), date("Y")));

$difference = (($today) - ($splitExpireDate));
$convertToDays = ($difference/86400);

echo $convertToDays;

Using MySQL:

SELECT (TO_DAYS(expire_date) - TO_DAYS(CURDATE())) as days_expired FROM tablename;