WordPress doesn’t generate a <link rel=”canonical” href=”http://www.yoursite.com”> by default.

This can cause issues with Google not indexing your page or indexing an incorrect canonical URL. You can get around this by adding your own canonical link to your site.

In order to do so, ensure you have created a child theme (see here on how to create your own WordPress child theme)

You’ll then need to copy the “header.php” file from the parent theme into your child theme’s folder and add the following code just before the <?php wp_head()?> code:

/** Add Canonical Tag **/
        $current_term = '';
	$canonical_url = '';

	if ( is_front_page() && is_main_query() ) 
	{
        /** We're On The Home Page **/
		$canonical_url = site_url();
	}
	elseif (is_category()) 
	{
        /** We're On A Category Page **/
		$current_term = get_queried_object();

		if ($current_term) 
		{
		  $canonical_url = get_term_link( $current_term );
		}
	}
	else
	{
        /** We're on a Post or Page **/
		 $canonical_url = get_permalink();
	}
        /** Echo out the canonical link to the header **/
	echo '';
	?>
	

Alternatively, you can add the code into your theme’s functions.php file if you don’t want to or can’t edit your header file.

In functions.php, add the following function:

function Insert_Canonical_In_Head() 
{
    global $post;
    /** Canonical Link **/
	echo '<!-- CANNONICAL LINK -->';
	echo ''. PHP_EOL;
	/** Add Canonical Tag Defaults**/
	$current_term = '';
	$canonical_url = '';
	if (is_home())
	{
		$canonical_url = site_url();
	}	
	else if (is_category()) 
	{
        /** We're On A Category Page **/
		$current_term = get_queried_object();

		if ($current_term) 
		{
		  $canonical_url = get_term_link( $current_term );
		}
	}
	else
	{
        /** We're on a Post**/
		 $canonical_url = get_permalink();
	}
        /** Echo out the canonical link to the header **/
	echo '<link rel="canonical" href="'.$canonical_url.'" />';
	echo ''. PHP_EOL;
	/** END Canonical Link **/
}

add_action( 'wp_head', 'Insert_Canonical_In_Head', 5 );