- var_dump: documentation ( source)
- date_default_timezone_set: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
date_default_timezone_set("Europe/London");
$dt = new DateTime("first day of this month");
var_dump($dt);
$dt->modify("-5 month");
var_dump($dt);
echo date('m/Y', strtotime("-5 month", strtotime("first day of this month")));