How to Create a dynamic Matrix visual using a date column to Assign Months

[LagSpencer]

I have the following data below 

I looking to create a matrix and dynamiclly assign forecast Month based on Support ready date

so for example Work Item 1230 forecast month 1 = july, forecast month 2 = Aug and so on

For Work Item 1456 Forcast month would =Sep

example on matrix trying to create

[vapid128 · Accepted solution]

NewMonth = 
var index = YEAR([Ready Date])*12+MONTH([Ready Date])+[ForcastMonth]-2
return int(index/12)&"-"&FORMAT(MOD(index,12)+1,"00")