title: Count number of products since last 30 days in google spreadsheet
body: <p>I have products I've sold which I would like to count for the last 30 days.</p>
  
  <p>I've tried this formula:</p>
  
  <pre><code>=COUNTIFS(C:C;"=My_Item";A:A;"&gt;=11 novembre 2014")
  </code></pre>
  
  <p>It works. But now, instead of <code>"11 novembre 2014"</code>,  I would like something like <code>"TODAY()-30"</code> but it keeps returning me <code>"0".</code> </p>
  
  <p>I assume it is a problem of date format but can't figure out what happens.</p>
  
  <p>Any ideas?</p>