day from two dates

function days_between($date1, $date2) {
  $tmp = DateTime::createFromFormat('Y-m-d', $date1);
  $start = $tmp->getTimestamp();
  $tmp = DateTime::createFromFormat('Y-m-d', $date2);
  $end = $tmp->getTimestamp();
  return round(($end - $start) / (60 * 60 * 24));
}