function daysDifference($endDate, $beginDate)
{
   //explode the date by "-" and storing to array
   $date_parts1=explode("-", $beginDate);
   $date_parts2=explode("-", $endDate);
   //gregoriantojd() Converts a Gregorian date to Julian Day Count
   $start_date=gregoriantojd($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;
}

Calcualte Day difference

PHP