In Excel Power Pivot, calculate month-over-month growth using a measure and DAX

In my Excel Power Pivot table I have a couple columns:

UsageMonth  (date datatype)
Consumed    (float number)

I want to calculate month-over-month growth. For example, if in January I consumed 100 and in February I consumed 110, 110/100-1 equals .10 or 10% growth.

If my table has this data:

UsageMonth   Consumed
1/1/2014          100
2/1/2014           110

I am thinking I should be able to create, in DAX, a measure named ConsumedPriorMonth. How do I do it?
RickInBellevueAsked:
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RickInBellevueAuthor Commented:
Okay, I figured out the answer to my own question.

To calculate month-over-month growth, the fundamental formula that underlies the solution is:

(Month2Usage - Month1Usage)/Month1Usage

The DAX-based answer has two parts:

Part 1: Create a measure that calculates the prior month's usage:

PriorMonthUsage:=CALCULATE(SUM(Usage),DATEADD(UsageData[UsageMonth],-1,MONTH))


Part 2:  Compute month-over-month growth:

MoMGrowth:=IF([PriorMonthUsage],(SUM([Usage])-[PriorMonthUsage])/[PriorMonthUsage],BLANK())

The IF/BLANK parts handles the case where there is no usage.
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