title: Date Arithmetic in PHP
body: <p>Is there a PHP function I can use to do something like the following:</p>
  
  <ul>
  <li>Get the date 6 months ago (e.g. now - 6 months)?</li>
  <li>Get the date 2 years from now (e.g. now + 2 years)?</li>
  </ul>