How to Display Related Posts in WordPress Without a Plugin

If you want related posts in WordPress without the overhead of a plugin like Related Posts for WP, you can build a simple version directly in your theme templates. Here is how.

Basic Related Posts by Category

This code goes in single.php (or the relevant template for your theme) after the_content():

<?php
$categories = get_the_category( get_the_ID() );

if ( ! empty( $categories ) ) {
    $category_ids = wp_list_pluck( $categories, 'term_id' );

    $related_args = array(
        'category__in'        => $category_ids,
        'post__not_in'        => array( get_the_ID() ),
        'posts_per_page'      => 3,
        'ignore_sticky_posts' => true,
        'orderby'             => 'rand',
    );

    $related_query = new WP_Query( $related_args );

    if ( $related_query->have_posts() ) :
        echo '<div class="related-posts">';
        echo '<h3>Related Articles</h3>';
        echo '<ul>';
        while ( $related_query->have_posts() ) :
            $related_query->the_post();
            printf(
                '<li><a href="%s">%s</a></li>',
                esc_url( get_permalink() ),
                esc_html( get_the_title() )
            );
        endwhile;
        echo '</ul></div>';
        wp_reset_postdata();
    endif;
}
?>

Related Posts by Tags

Replace the category query with a tag query:

$tags = get_the_tags( get_the_ID() );

if ( ! empty( $tags ) ) {
    $tag_ids = wp_list_pluck( $tags, 'term_id' );

    $related_args = array(
        'tag__in'             => $tag_ids,
        'post__not_in'        => array( get_the_ID() ),
        'posts_per_page'      => 3,
        'ignore_sticky_posts' => true,
    );
    // ... rest of the query
}

Adding Transient Caching

Related post queries run on every single post page load. On high-traffic sites, this adds significant database load. Cache the results using WordPress transients:

<?php
$post_id         = get_the_ID();
$transient_key   = 'related_posts_' . $post_id;
$related_posts   = get_transient( $transient_key );

if ( false === $related_posts ) {
    $categories    = get_the_category( $post_id );
    $category_ids  = wp_list_pluck( $categories, 'term_id' );

    $related_query = new WP_Query( array(
        'category__in'   => $category_ids,
        'post__not_in'   => array( $post_id ),
        'posts_per_page' => 3,
        'fields'         => 'ids', // Only retrieve IDs for caching
    ) );

    $related_posts = $related_query->posts;
    set_transient( $transient_key, $related_posts, DAY_IN_SECONDS );
    wp_reset_postdata();
}

if ( ! empty( $related_posts ) ) {
    echo '<div class="related-posts"><h3>Related Articles</h3><ul>';
    foreach ( $related_posts as $post_id ) {
        printf(
            '<li><a href="%s">%s</a></li>',
            esc_url( get_permalink( $post_id ) ),
            esc_html( get_the_title( $post_id ) )
        );
    }
    echo '</ul></div>';
}
?>

The transient stores related post IDs for 24 hours, so the database query runs at most once per day per post rather than on every page view.

When to Use a Plugin Instead

This manual approach works well for simple related posts by category or tag. Use a dedicated plugin like Related Posts for WP when you need: matching across multiple taxonomies simultaneously, a more sophisticated relevance algorithm, a visual management interface, or RSS feed related posts. The plugin also handles edge cases (no matching posts, recently published posts without taxonomy terms) more gracefully than a basic custom query.

For custom related post implementations using machine learning similarity, custom post type support, or integration with search engines like ElasticSearch, a WordPress developer can build a tailored solution.