Rolling 12 Month total by customer

[mpg06]

Need to get sum of quantity for previous 12 months by Customer. For instance: For Customer 1 July 2016 total should be from August 2015 - July 2016. This should be grouped by customer. If 12 months prior data does not exist, it can be 0 or blank.  Is it possible to calculate a column or measure? Thanks!

Customer	Date	Quantity	Expected Result
1	1/1/2015	1	0
1	2/1/2015	2	0
1	3/1/2015	4	0
1	4/1/2015	2	0
1	5/1/2015	1	0
1	6/1/2015	2	0
1	7/1/2015	1	0
1	8/1/2015	3	0
1	9/1/2015	4	0
1	10/1/2015	1	0
1	11/1/2015	1	0
1	12/1/2015	1	23
1	1/1/2016	1	23
1	2/1/2016	1	22
1	3/1/2016	1	19
1	4/1/2016	2	19
1	5/1/2016	4	22
1	6/1/2016	2	22
1	7/1/2016	1	22
2	1/1/2015	2	0
2	2/1/2015	1	0
2	3/1/2015	3	0
2	4/1/2015	4	0
2	5/1/2015	1	0
2	6/1/2015	1	0
2	7/1/2015	1	0
2	8/1/2015	1	0
2	9/1/2015	1	0
2	10/1/2015	1	0
2	11/1/2015	1	0
2	12/1/2015	1	18
2	1/1/2016	1	17
2	2/1/2016	1	17
2	3/1/2016	1	15
2	4/1/2016	1	12
2	5/1/2016	1	12
2	6/1/2016	1	12
2	7/1/2016	1	12
2	8/1/2016	1	12

[mike_honey]

This is a common requirement that you would expect to be easily solved with a single function or formula.  But unfortunately DAX is saddled with several shockingly poor design decisions in this area, that have still not been corrected many years later.

For a glimpse of the full horror, try this article:

http://www.sqlbi.com/articles/rolling-12-months-average-in-dax/

Note it breezily assumes you start with a tidy Calendar table which in your case will need to extend 12 months prior to your earliest date. 

Personally I would go back to the Edit Queries layer and resolve it there - the tool behaves more rationally and predictably there.

[mpg06]

I tried all of that, din't work. The closest I came to the solution was using code below from one of the forum discussions: It gives me 

Cumulative2 = VAR RowDate = Sheet1[Date]
VAR RowCust = Sheet1[Customer]
RETURN
    CALCULATE (
        SUM ( Sheet1[Quantity] ),
        FILTER (
            Sheet1,
            MONTH(RowDate) - Month(Sheet1[Date])<=12
                && YEAR ( RowDate) - YEAR ( Sheet1[Date] )<=1 && Sheet1[Customer] = RowCust
        ), VALUES(Sheet1[Customer])
    )

[mike_honey]

Your results look really odd, and nothing like the expected results you originally posted. For example your first row shows 35, where you expected 0.