Take a look at these posts and see if that works for you.
Since you are working with months, you may want to replace the Year value with Months, but you will need to add a divide by 12 to convert it to years.
In the end, you will have a date in the future in that math column and you can then use additional math columns to split out Month(date) and Year(date), then use a template column to put it back together however you want.