Get previous/next month php

next-prev-month.php

<?php
// Number of months after/before
    $num = 3;
    // Months before
    $now = new DateTime();
    $lastMonth = $now->sub(new DateInterval('P'. $num . 'M'));
    // displays month/s before
    echo $lastMonth->format('Y M');
    // quick and short way
    echo date('M', strtotime("-". $num . " month"));

    // Months after
    $nextMonth = $now->add(new DateInterval('P'. $num . 'M'));
    // displays month/s after
    echo $nextMonth->format('Y m');
    // quick and short way
    echo date('M', strtotime("+". $num . " month"));