title: Rolling 12 Month sum in PowerPivot
body: <p>In PowerPivot Excel 2016 I write a formula for rolling 12 month sum of sales as below :</p>
  
  <pre class="lang-dax prettyprint-override"><code>Rolling Sum:=CALCULATE (
  [Sales] ,
  DATESBETWEEN (
      Sales[Date],
      FIRSTDATE(DATEADD(Sales[Date],-365,DAY)),
      LASTDATE (Sales[Date] )
   )
  )
  </code></pre>
  
  <p>But it seems not working correctly. for each month it shows me only sales of that month!
  Does anybody knows how should I fix my problem?!</p>
  
  <p>Thanks In Advance</p>