title: SSRS 2016 - How to calculate a percentage difference between two values in a group?
body: <p>I'm creating a report that shows the sales of item before a date range and after a date range. </p>
  
  <p>The part I ran into trouble with is the percentage difference between the total sales on Date 1 and Date 2.</p>
  
  <p>Items can have no sales for a certain week.
  The user can select multiple item ID's in the item ID parameter.</p>
  
  <p>I can update the question to post my SQL query if needed.</p>
  
  <p><strong>What I've tried</strong></p>
  
  <p>Since I put a group on item ID I thought the <code>First</code> and <code>Last</code> functions would work.</p>
  
  <p>Here's my expression on the column PCT.</p>
  
  <p><code>=(Last(Fields!total_sales1.Value, "Date1")- First(Fields!total_sales1.Value, "Date1")) / First(Fields!total_sales1.Value, "Date1") * 100</code></p>
  
  <p>But when I run the report I get the following results.</p>
  
  <p><a href="https://i.stack.imgur.com/Yy8Tg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Yy8Tg.png" alt="enter image description here"></a></p>
  
  <p>I need an expression on PCT column that will give me a percentage difference for each item pairs.</p>