title: Excel Formula: Count cells where value is date
body: <p>I'm looking for a formula to run a COUNTIF (or similar) on a range of cells, and where the contained value is a date, to increment the counter - essentially something like:</p>
  
  <pre><code>=COUNTIF(range, if_date())
  </code></pre>
  
  <p>What I haven't been able to find is a logical test for the if_date() part of the question. Is there a way to test a cell to check whether its content is a date?</p>