Related Posts By Category For Single.php, Exclude Current Single Post

Show a loop of related articles on the sidebar of single.php (or any single post template sidebar), but exclude the current single post from the related loop. This code goes in the sidebar of a single template file of a WordPress theme. Related articles, for this code, are posts within the same category of the current single post being viewed. (To get related posts of custom post types, see Get Related Posts For Custom Post Type By Category. )

In the example below, you can modify the HTML on line 25 to display the thumbnails, and/or excerpts, depending on your preferences. Left as it, it will show a list of the titles of 3 related posts.

<?php
$categories = get_the_category($post->ID);
if ( $categories ) {
	$category_ids = array();
	foreach ( $categories as $individual_category ) {
		$category_ids[] = $individual_category->term_id;
	}
	$args=array(
		'category__in' => $category_ids,
		'post__not_in' => array($post->ID),
		'showposts'=>3, // Number of related posts that will be shown.
		'ignore_sticky_posts'=>1
	);
	$my_query = new wp_query( $args );
	if( $my_query->have_posts() ) {
		
		echo '<h3>Related Articles</h3>'; // You can edit this
		echo '<ul>';

		while ($my_query->have_posts()) {
			$my_query->the_post();
			?>
			<!-- do stuff -->

			<li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li>

			<?php
		}

		echo '</ul>';
	
	}
}
?>