Use the time function to get the current timestamp

<?php
$nextWeek = time() + (7 * 24 * 60 * 60);      //7 days; 24 hours; 60 mins; 60secs
echo 'Now: '. date('Y-m-d') ."<p>";
echo 'Next Week: '. date('Y-m-d', $nextWeek);
?>