Variance sales between rows

Hi.

You'll can use a Calculated Measure to return the Previous Period's sales, and compare it with your Current Period Sales. 

If you are using a Date Table, try the following Measure:

Variance = SUM('Table'[Sales]) - CALCULATE(SUM('Table'[Sales]), DATEADD('Table'[Date], -1, MONTH))

If you are not using a Date Table, you should implement one according to a guide like this:

How to Create a Date Table in Power BI | Master Data Skills + AI (enterprisedna.co)

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