<?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";
}
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