DateTime and DateInterval Function

date_class.php

<?php

function getDateFromNow($interval='P1D', $direction='add') {

	$currentDate = new DateTime;
	$intervalDate = new DateInterval($interval);

	if ($direction == 'sub') {
		$resultDate = $currentDate->sub($intervalDate);
	} else {
		$resultDate = $currentDate->add($intervalDate);
	}

	return $resultDate->format('Y-m-d H:i:s');
}