Add Additional Row to Table

I have the below table (and worksheet attached) showing the number of records that exist for each month with each year in its own column. Is it possible to add an additional row to this table that will show just a calculation of the previous months of the year up to the current month? Call this YTD.

For example if I looked at this report for February, this additional row would report 2 for Febuary 2014 and 4 for February 2015.

I think my YTD calculation would be WINDOW_SUM([Number of Records],FIRST(),0). I just don't know how to add that as a seperate row on the existing table. I need all months listed all the time and then the YTD value would just change based on whatever current month it is.