- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$month=12;
$year=2014;
$startdate = strtotime($month.'/1/'.$year);
$stopdate = strtotime('last day of this month ',$startdate);
echo (date('Y-m-d',$startDate).' - '.date('Y-m-d',$stopDate));