<?php

$start = new DateTimeImmutable('2018-01-31');

echo $start->modify('+1 month')->format('Y-m-d') . "\n\n";

$period = new DatePeriod($start, new DateInterval('P1M'), 2);

foreach ($period as $date) {
	
   echo $date->format('Y-m-d') . "\n";
	
}