WordPress – Progressive discount Woocommerce product price based on quantity thresholds

Exceptionally, I answer your question as we expect from you to provide a real code attempt in your question. Also next time, ask one question at the time, it’s the rule on Stack OverFlow.

So, the following code will answer to your 2 question. It will chnage the product price based on quantity thresholds, for specific products.

In the first function, you will define in the array the targeted product Ids.

In The 2nd function, you will set your quantity thresholds and price rates.

This code works for simple products (not for variable products / product variations):

// Conditional function - Settings: Define your product IDS HERE
function is_product_threshold_qty_pricing_enabled( $product ){
    // Here set in the array your product IDS
    $targeted_product_ids = array(15, 16, 17, 18, 24);

    return in_array($product->get_id(), $targeted_product_ids);
}

// Utility function - Settings: Define your threshold quantity and price rates (for pricing)
function get_quantity_threshold_price_rate( $quantity ) {
    if ( $quantity < 100 ) {
        $rate = 1; // No discount (less than 100)
    } elseif ( $quantity < 200 ) {
        $rate = 0.7; // - 30% discount (between 100 and 199 )
    } else {
        $rate = 0.5; // - 50% discount (up to 200)
    }
    return $rate;
}

// Utility function: Get threshold quantity pricing for display
function get_displayed_qty_threshold_pricing( $product, $quantity ) {
    $price_rate = get_quantity_threshold_price_rate( $quantity );
    if ( $price_rate < 1 ) {
        $regular_price = wc_get_price_to_display( $product, array( 'price' => $product->get_regular_price() ) );
        $active_price  = wc_get_price_to_display( $product, array( 'price' => ($product->get_price() * $price_rate) ) );

        $price = wc_format_sale_price( $regular_price, $active_price ) . $product->get_price_suffix();
    } else {
        $price = $product->get_price_html(); // No discount
    }
    error_log('[ '.$price_rate.' ] quantity: '.$quantity . ' | price: ' . wp_strip_all_tags($price));
    return $price;
}

// PHP Admin Ajax receiver: Return formatted prices
add_action('wp_ajax_qty_threshold_pricing', 'get_qty_threshold_pricing');
add_action('wp_ajax_nopriv_qty_threshold_pricing', 'get_qty_threshold_pricing');
function get_qty_threshold_pricing() {
    if (isset($_POST['product_id']) && isset($_POST['quantity'])) {
        $product = wc_get_product(intval($_POST['product_id'])); // GET THE PRODUCT OBJECT

        echo get_displayed_qty_threshold_pricing( $product, intval($_POST['quantity']) );
    }
    wp_die(); // Exit silently (to avoid an Error 500)
}

// Jquery Ajax: Display on single product pages the price based on quantity
add_action('wp_footer', 'display_single_product_threshold_pricing', 10);
function display_single_product_threshold_pricing() {
    global $product;

    if( is_product() && is_product_threshold_qty_pricing_enabled( $product ) ) :
    ?>
    <script>
    jQuery(function($){
        const blockWhite = {message: null, overlayCSS: {background: '#fff', opacity: 0.6}};
        $('form.cart').on('change input', '[name=quantity]', function() {
            $('form.cart').block(blockWhite);
            $.ajax({
                url:  '<?php echo admin_url( 'admin-ajax.php' ); ?>',
                type: 'POST',
                data: {
                    'action':     'qty_threshold_pricing',
                    'product_id': '<?php echo $product->get_id(); ?>',
                    'quantity':   $(this).val()
                },
                success: function(response) {
                    $('form.cart').unblock();
                    $('.price').html(response);
                }
            });
        });
    });
    </script>
    <?php
    endif;
}

// Display cart item updated price in Cart and Mini Cart
add_action('woocommerce_cart_item_price', 'filter_minicart_displayed_price', 10, 2);
function filter_minicart_displayed_price($price, $cart_item) {
    $product = wc_get_product( $cart_item['data']->get_id() );
    if ( is_product_threshold_qty_pricing_enabled( $product ) ) {
        $price = get_displayed_qty_threshold_pricing( $product, $cart_item['quantity'] );
    }
    return $price;
}

add_action('woocommerce_before_calculate_totals', 'set_cart_item_updated_price');
function set_cart_item_updated_price($cart) {
    if ((is_admin() && !defined('DOING_AJAX')))
        return;

    if (did_action('woocommerce_before_calculate_totals') >= 2)
        return;

    // Loop through cart items and set the updated price
    foreach ($cart->get_cart() as $cart_item) {
        if ( is_product_threshold_qty_pricing_enabled( $cart_item['data'] ) ) {
            $price_rate = get_quantity_threshold_price_rate( $cart_item['quantity'] );
            if ( $price_rate < 1 ) {
                $product = wc_get_product($cart_item['data']->get_id());

                $cart_item['data']->set_price( $product->get_price() * $price_rate );
                $cart_item['data']->set_sale_price( $product->get_sale_price() * $price_rate );
            }

        }
    }
}

Code goes in functions.php file of your child theme (or in a plugin). Tested and works.

Addition:

To target product categories (or product tags) instead of product IDs, replace the first function with:

function is_product_threshold_qty_pricing_enabled( $product ){
    // Here set in the array the term slugs
    $term_slugs = array('hoodies', 't-shirts');
    $taxonomy   = 'product_cat'; // Product category taxonomy

    $product_id = $product->is_type('variation') ? $product->get_parent_id() : $product->get_id();

    return has_term( $term_slugs, $taxonomy, $product_id );
}

For product tags, replace 'product_cat' with 'product_tag'.