HOW DO I ADD 6 MONTHS TO CURRENT DATE!

You received some good information. Let me add some general thoughts: When it comes to dates in Acrobat's JavaScript, you are dealing with "normal" JavaScript, and can research how this particular problem can be solved in JavaScript - without having to limit your search to Acrobat. The "Date" object is part of the core JavaScript language. Any JavaScript implementation consists of two parts: The core language and any potential domain specific extensions. In the web browser, these extensions would deal with web pages and HTML, wheras in Acrobat these exensions are all about PDF documents. But both implementations would provide the same level of support for the Date object - and therefore date specific manipulations. 

You can use this as custom calculation script of Expiry date field:

var today = this.getField("_Date").valueAsString;
if(today == "") event.value = "";
else{
var sixmonth = util.scand("mm/dd/yyyy", today);
sixmonth.setMonth(sixmonth.getMonth()+6);
event.value = util.printd("mm/yyyy", sixmonth);}

Read this:

https://community.adobe.com/t5/acrobat/js-code-for-3-6-month-to-add-to-a-date-date-of-employment/td-p/9704149?page=1 

The price "day" is not important.

I am more interested in the 'month' and 'Year'.