DAX formula help!! (Calculating rolling 3 months)

I am trying to calculate the rolling three months sum for a particular table. For Example I have a Pivot table I built similar to this:

1/31/2015 10
2/28/2015 5
3/31/2015 4
4/30/2015 3
5/31/2015 2
6/30/2015 5
7/31/2015 6
8/31/2015 7
9/30/2015 2
10/31/2015 3
11/30/2015 5
12/31/2015 4

Each date has a corresponding number i.e. Sum(Values)... For each of the date, I don't want the sum for THAT month, but instead want the sum of that month PLUS the two prior month and have it show up in that current month.

For example in row 12/31/2015 you will see 12 (4+5+3)
in 11/30/2015 you will see 10 (5+3+2)
in 10/31/2015 you will see 12 (3+2+7)
etc, etc, etc...

How do I write this DAX formula so I am pulling in the rolling three month value for that month??

Thanks!

Are you looking to add a new column with the rolling three month total, or are you looking to replace your existing column? If it's the latter, where are those (current) values coming from?