<?php 
function add_date($orgDate,$mth){ 
  $cd = strtotime($orgDate); 
  $retDAY = date('Y-m-d', mktime(0,0,0,date('m',$cd)+$mth,date('d',$cd),date('Y',$cd)));
   return $retDAY; 
} 
?> 

function daysInterval($low_date, $high_date)
    {
        $days = array();
        
        $day_step = 60*60*24;
   
        for ($d=$low_date; $d<=$high_date; $d=$d+$day_step)
        {
            $days[mktime(0,0,0, date('m', $d), date('d', $d), date('Y', $d))] = date('d', $d);
        }
        
        return $days;
    }