Best way is use DateTime object to convert your date.
$regDate = "Jan / 2013";
$myDateTime = DateTime::createFromFormat('M / Y', $regDate);
$myDateTime->modify('+6 Months');
echo $myDateTime->format('M / Y');
Note: It will support for PHP 5 >= 5.3.0 only.
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solved how to get after 6 month date in M / Y format?