Loop for related posts by category

related-posts-loop.php

<?php
// Loop for related posts by category 
 
// Get all categories for current post
$categories = get_the_category();
 
if ($categories) { ?>
 
  <?php foreach ( $categories as $category ) {
 
    $category_id = $category->cat_ID;
 
    $args = array (
      'cat' => $category_id,
    );
 
    // Set up a variable to call new WP_Query
    $loop = new WP_Query( $args );
 
    // Start the loop
    while ($loop->have_posts()) : $loop->the_post(); ?>
 
        <a href="<?php the_permalink() ?>"><h4><?php the_title() ?></h4></a>
 
    <?php 
    // End post loop
    endwhile;
 
  } // End foreach category
 
} // End if categories
 
// Rewind the posts so we can have more loops in the page
rewind_posts() ?>