How to Get the Category of a Post by ID in WordPress Without Plugins

Sometimes you need to display a post’s category outside the main loop or in a custom function. WordPress makes this easy with its built-in `get_the_category()` function. In this quick guide, you’ll learn how to get the category of any post by its ID — no plugins required.

Step 1: Open Your functions.php File

Start by opening your theme’s `functions.php` file, located in your current theme directory (usually `wp-content/themes/your-theme/functions.php`). This is where we’ll define our custom helper function.

Step 2: Create the Function

Now, we’ll define a function that takes a post ID and returns the name of its first associated category. Add this code to your `functions.php` file:

1function get_post_category_by_id( $post_id ) {
2      // Get all categories for the post
3      $categories = get_the_category( $post_id );
4  
5      // Check if categories exist
6      if ( ! empty( $categories ) ) {
7          // Return the first category name
8          return $categories[0]->name;
9      }
10  
11      // Return false if no categories found
12      return false;
13  }

This function uses `get_the_category()` to retrieve all categories linked to the post. It then returns the first category name if one exists, or `false` if no categories are found. You can easily modify this to return all categories or specific details like category IDs or slugs.

Step 3: Use the Function in Your Template

Now that the function is ready, you can call it anywhere in your theme. Just pass the post ID as a parameter:

1$post_id = 123; // Replace with your post ID
2  $category_name = get_post_category_by_id( $post_id );
3  
4  if ( $category_name ) {
5      echo 'The category of the post is: ' . esc_html( $category_name );
6  } else {
7      echo 'No categories found for this post.';
8  }

This example displays the category name directly on the page. Replace `123` with a real post ID or use it dynamically inside a loop (for example, `$post->ID`).

Complete Example

1<?php
2  // Define the function
3  function get_post_category_by_id( $post_id ) {
4      $categories = get_the_category( $post_id );
5  
6      if ( ! empty( $categories ) ) {
7          return $categories[0]->name;
8      }
9  
10      return false;
11  }
12  
13  // Use it in your theme
14  $post_id = 123; // Replace with your post ID
15  $category_name = get_post_category_by_id( $post_id );
16  
17  if ( $category_name ) {
18      echo 'The category of the post is: ' . esc_html( $category_name );
19  } else {
20      echo 'No categories found for this post.';
21  }

You can place this code in your theme templates or inside a shortcode for flexible display. To show multiple categories, loop through the `$categories` array instead of returning only the first element.

Useful Links

WordPress Developer Reference – get_the_category():

Category functions overview:

And that’s all there is to it! You now know how to retrieve a post’s category by ID without using any plugins. Whether you’re building a custom post display or tweaking a theme layout, this snippet will come in handy time and again. Keep coding and experimenting!