To add a number of months to a date, first get the month using getMonth() method and add a number of months.
Example
You can try to run the following code to add a number of months
Live Demo
<!DOCTYPE html>
<html>
<body>
<script>
var d, e;
d = new Date();
document.write(d);
e = d.getMonth()+1;
document.write("<br>Incremented month = "+e);
</script>
</body>
</html>