title: Display php date calculation, with a shortcode
body: <p>Trying to display "XX Year in the Industry" text on a CPT. The idea is that the client would enter the year the staff member started in a custom field and an automatic calculation would subtract that # from the current year and display. </p>
  
  <p>The basic math is: Current year - Entered start year = Displayed year</p>
  
  <p>This is almost working... but the calculation doesn't happen. The shortcode works, but not the calculation. Am I missing a filter? Do I maybe need 2 functions, one for the shortcode and one for the calc?</p>
  
  <pre><code>function YearsIndustry_shortcode($metadata, $object_id, $meta_key, $single) {
     $start_year = get_post_meta( $post_id, 'ptb_start_year' );
     $current_year = new DateTime("now");
     $displayed_year = date_diff($current_year, $start_year)-&gt;y;
     $Years = $displayed_year. 'Years in Industry';
     return $Years;
  }
  add_shortcode('YII', 'YearsIndustry_shortcode');
  </code></pre>