The way I would do this is I would first create a calculated metric for average monthly visits by doing visits (or sessions because I'm using CJA) divided by a distinct count of months.

Then you can put this in your table and add a time period column for YoY. Then from the table you just do a bar chart (or line, or whatever viz you want).


One thing to keep in mind with this, make sure your date ranges are full months so that you get an accurate average. But using the count of months will account for if you change your date range from 3 to 4 months, for example. Otherwise you could always just do visits divided by 3, if it's always going to be 3 months.