function dateDiff($beginDate, $endDate) {
	$fromDate = date('Y-n-j',strtotime($beginDate));
	$toDate = date('Y-n-j',strtotime($endDate));
	$date_parts1=explode('-', $beginDate);
	$date_parts2=explode('-', $endDate);
	$start_date=gregoriantojd($date_parts1[1], $date_parts1[2], $date_parts1[0]);
	$end_date=gregoriantojd($date_parts2[1], $date_parts2[2], $date_parts2[0]);
	return $end_date - $start_date;
}

http://www.klovera.com/php-subtract-dates/

// example <br>
$from = '2011-1-6'; <br>
$to = '2011-1-8'; <br>
dateDiff($from,$to); // returns 2

Number of days between 2 dates

php

PHP