/**
 * Returns an array with the dates between to dates given.
 *
 * @link http://us3.php.net/manual/en/function.date.php#AEN25217
 * 
 * @param mixed $startdate Timestamp or strtotime() recognizeable string
 * @param mixed $enddate Timestamp or strtotime() recognizeable string
 * @param string[optional] $format date() format string
 * @return mixed Array of timestamps or dates if given format
 */
public static function dates_between($startdate, $enddate, $format=null){

    (is_int($startdate)) ? 1 : $startdate = strtotime($startdate);
    (is_int($enddate)) ? 1 : $enddate = strtotime($enddate);

    if($startdate > $enddate){
        return false; //The end date is before start date
    }

    while($startdate < $enddate){
        $arr[] = ($format) ? date($format, $startdate) : $startdate;
        $startdate += 86400;
    }
    $arr[] = ($format) ? date($format, $enddate) : $enddate;

    return $arr;
}

Obtener las fechas que hay entre dos fechas dadas. No es la diferencia de días o similares, sino las fechas en sí.

Fechas entre dos fechas

PHP