// returned $date Y/m/d
function work_days_from_date($days, $forward, $date=NULL) 
{
    if(!$date)
    {
        $date = date('Y-m-d'); // if no date given, use todays date
    }

    while ($days != 0) 
    {
        $forward == 1 ? $day = strtotime($date.' +1 day') : $day = strtotime($date.' -1 day');
        $date = date('Y-m-d',$day);
        if( date('N', strtotime($date)) <= 5) // if it's a weekday
        {
          $days--;
        }
    }
    return $date;
}