Calculate Cumulative Measure

I have 2 measures that I would like to change to calculate as cumulative totals.

The first measure is calculating total quantity sold, and the second is calculating total quantity sold last year.

1. SUM QTY = sum('Sales Data'[QTY])  

2. Qty Sold LY = CALCULATE([SUM QTY], DATEADD(DateTable[Date], -1, YEAR))

When I put them into a graph by month, it shows the quantity by each month.

I would like it to add the values together so that Jan would be Jan, Feb would be Jan+Feb, March would be Jan+Feb+March, etc.....

Right now this is the chart I have:

The cumulative quantity chart would look more like a line that is up and to the right, as opposed to fluctuating.

If anyone knows how to change the chart to go by cumulative total by month, that would be appreciated.

Thanks for the help!