title: SSRS - Sum Last 12 items
body: <p>I have a Total column and am summing all the values in the row with:</p>
  
  <p><code>=Sum(Fields!MyField.Value)</code></p>
  
  <p><strong>How can I sum only the last 12 items?</strong></p>
  
  <p>This is valid:</p>
  
  <p><code>=Last(Fields!MyField.Value)</code></p>
  
  <p>I need something like the below...</p>
  
  <p><code>=Sum( LastX(Fields!MyField.Value, 12) )</code></p>