PHP Syntax Error

What is wrong with the following PHP?
If my url is:
http://www.MYSITE.com/file.php?d=2013-09-08
Why does the following not work?

if ((isset($_GET['d']))) {
	$rd = $_GET['d'];
	$requestDate = date($rd, strtotime("+2 weeks"));
	echo '<h1>NEW DATE: '.$requestDate.'</h1>';
}

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it always echo's; 2013-09-08
There is something wrong with the way I am formatting:
$requestDate = date($rd, strtotime("+2 weeks"));