How to Automatically Add Related Products to the Cart in WooCommerce – 2026

/*
 * Snippet: How to Automatically Add Related Products to the Cart in WooCommerce – 2026
 * Author: John Cook 
 * URL: https://wcsuccessacademy.com/?p=1777
 * Tested with WooCommerce 10.7.0
 * "This function automatically adds related products to the cart when specific products are added"
*/
function wcsuccess_add_related_products_to_cart( $cart_item_key, $product_id, $quantity, $variation_id, $variation, $cart_item_data ) {
    // Define which products should trigger the automatic addition of related products
    $trigger_product_ids = array( 25, 30 ); // Replace with your product IDs

    // Define the related products to add when the trigger products are added
    $related_products = array(
        25 => array( 50, 51 ), // When product 25 is added, add products 50 and 51
        30 => array( 52 ), // When product 30 is added, add product 52
    );

    // Check if the product that was added to the cart is in the trigger list
    if ( in_array( $product_id, $trigger_product_ids ) ) {
        if ( ! empty( $related_products[ $product_id ] ) ) {
            foreach ( $related_products[ $product_id ] as $related_product_id ) {
                // Check if the related product is already in the cart
                if ( ! wcsuccess_is_product_in_cart( $related_product_id ) ) {
                    WC()->cart->add_to_cart( $related_product_id );
                }
            }
        }
    }
}
add_action( 'woocommerce_add_to_cart', 'wcsuccess_add_related_products_to_cart', 10, 6 );

/*
 * Snippet: How to Automatically Add Related Products to the Cart in WooCommerce – 2026
 * Author: John Cook 
 * URL: https://wcsuccessacademy.com/?p=1777
 * Tested with WooCommerce 10.7.0
 * "This function checks if a product is already in the cart"
*/
function wcsuccess_is_product_in_cart( $product_id ) {
    foreach ( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
        if ( $cart_item['product_id'] == $product_id ) {
            return true;
        }
    }
    return false;
}

$trigger_product_ids = array( 45, 50 ); // New trigger products
$related_products = array(
    45 => array( 60, 61 ), // When product 45 is added, add products 60 and 61
    50 => array( 62 ), // When product 50 is added, add product 62
);

/*
 * Snippet: How to Automatically Add Related Products to the Cart in WooCommerce – 2026
 * Author: John Cook 
 * URL: https://wcsuccessacademy.com/?p=1777
 * Tested with WooCommerce 10.7.0
 * "This function adds a notification message when related products are automatically added"
*/
function wcsuccess_notify_related_products_added() {
    if ( ! is_cart() ) {
        return;
    }

    if ( WC()->session->get( 'related_products_added' ) ) {
        wc_print_notice( __( 'Related products have been added to your cart.', 'woocommerce' ), 'notice' );
        WC()->session->__unset( 'related_products_added' );
    }
}

add_action( 'woocommerce_before_cart', 'wcsuccess_notify_related_products_added' );

/*
 * Snippet: How to Automatically Add Related Products to the Cart in WooCommerce – 2026
 * Author: John Cook 
 * URL: https://wcsuccessacademy.com/?p=1777
 * Tested with WooCommerce 10.7.0
 * "This function sets a session variable when related products are added"
*/
function wcsuccess_set_related_product_session( $cart_item_key, $product_id, $quantity, $variation_id, $variation, $cart_item_data ) {
    WC()->session->set( 'related_products_added', true );
}
add_action( 'woocommerce_add_to_cart', 'wcsuccess_set_related_product_session', 10, 6 );

/*
 * Snippet: How to Automatically Add Related Products to the Cart in WooCommerce – 2026
 * Author: John Cook 
 * URL: https://wcsuccessacademy.com/?p=1777
 * Tested with WooCommerce 10.7.0
 * "This function displays the related products on the product page before adding them to the cart"
*/
function wcsuccess_display_related_products_on_product_page() {
    global $product;

    $product_id = $product->get_id();

    $related_products = array(
        25 => array( 50, 51 ), // When product 25 is added, display products 50 and 51
        30 => array( 52 ), // When product 30 is added, display product 52
    );

    if ( ! empty( $related_products[ $product_id ] ) ) {
        echo '<div class="related-products-banner" style="background-color: #f4f4f9; padding: 20px; text-align: center; margin-bottom: 20px;">';
        echo '<h2>Related Products You’ll Get</h2>';
        foreach ( $related_products[ $product_id ] as $related_product_id ) {
            $related_product = wc_get_product( $related_product_id );
            echo '<p><strong>' . esc_html( $related_product->get_name() ) . '</strong></p>';
        }
        echo '</div>';
    }
}
add_action( 'woocommerce_before_add_to_cart_form', 'wcsuccess_display_related_products_on_product_page' );