<?php

$now = new DateTime();
echo "now = ", $now->format("Y-m-d"), "\n";

$yesterday = $now->modify('-1 day');
$tomorrow = (new DateTime())->modify('+1 day');
$nextMonth = new DateTime('+1 month');
$nextYear = new DateTime('+1 year');

echo "yesterday = ", $yesterday->format("Y-m-d"), "\n";
echo "tomorrow = ", $tomorrow->format("Y-m-d"), "\n";
echo "nextMonth = ", $nextMonth->format("Y-m-d"), "\n";
echo "nextYear = ", $nextYear->format("Y-m-d"), "\n";

echo "now after modify = ", $now->format("Y-m-d"), "\n";