Formula for cumulate sales 12 month back

Hi experts,

I'm using the power BI tool since last year and i build very nice and intresting reports. Now, I want to build a graph which will show me the trends of the sales for the current year in a specific way; actually what I'm trying to do is to compare by months the cumulate sales from today, back 12 months for the last 2 years.

So the graph will show me on the x axis the months and on the Y axis the Sales **bleep** last 12 Months

What i'm asking you is  to calculate the sum of sales of last 12 months for each month

Thanks in advance