- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$lastmonday = strtotime('last monday of this month');
$lmonday = date('Y-m-d',$lastmonday);
$firstday = strtotime('first day of this month');
$fday = date('Y-m-d',$firstday);
$d1 = new DateTime($lmonday);
$dd1 = $d1->format('Y-m-d');
$d2 = new DateTime($fday);
$dd2 = $d2->format('Y-m-d');
$period_serv = $dd1->diff($dd2);
$theperiod = $period_serv->format('%a');
echo $theperiod;