title: how to calculate a difference between two Zend_Date objects, in months
body: <p>I have two objects of <code>Zend_Date</code> class and I want to calculate the difference between them in full calendar months.. How can I do this?</p>
  
  <pre><code>&lt;?php
  $d1 = new Zend_Date('1 Jan 2008');    
  $d2 = new Zend_Date('1 Feb 2010');
  $months = $d1-&gt;sub($d2)-&gt;get(Zend_Date::MONTH);
  assert($months == -25); // failure here
  </code></pre>
  
  <p>Thanks in advance!</p>