Calculate Extended Rolling Average using previous 5 months data

[Anonymous]

Hello

I am trying to calculate the projected rolling average using the previous months data as in my table below.

e.g.
I have the data for car sales January to September, but I would like to estimate the values for October-December using the last five months rolling average.
So October will use the sales from (May-September), November will use the sales from (June - Septmber + the rolling average calculated for October)...and so on.

I would like to extend it to 2021 as well - So that I can use the projected values in the 2021 table as well.

The problem I am facing is if I write a measure for the data to calculate the rolling averages - my 2021 table breaks as it cannot access the calculated measure for 2020 ?

Can you please help me with the dax query?

Thanks in advance