woocommerce_before_calculate_totals

This action runs before WooCommerce calculates cart totals, giving developers access to the current cart items and their product objects for adjustments.

Quick Reference

How It Works

WooCommerce calls do_action() during WC_Cart::calculate_totals() and passes the cart object. A callback can inspect items before totals are calculated. Totals may be recalculated more than once per request, so avoid multiplying or repeatedly reducing an already modified price.

PHP Example

add_action( 'woocommerce_before_calculate_totals', function ( $cart ) {
    if ( is_admin() && ! wp_doing_ajax() ) {
        return;
    }

    foreach ( $cart->get_cart() as $item ) {
        if ( 123 === (int) $item['product_id'] ) {
            $item['data']->set_price( 19.00 );
        }
    }
} );

Replace product ID 123 and the price with values appropriate to your store. This sets an absolute unit price, avoiding repeated percentage adjustments during recalculation.

Add the code to a site-specific plugin or a child theme's functions.php file, then test it on a staging site.

Common Pitfalls

WooCommerce may calculate totals several times as a shopper updates the cart or checkout. Repeatedly subtracting a percentage from $item['data']->get_price() can make a discount grow on each pass. The example sets a fixed price instead, so rerunning it produces the same result. Do not call $cart->calculate_totals() from this callback, since that can start the same calculation again.

For a variation, $item['product_id'] identifies its parent product, while $item['variation_id'] identifies the specific variation. The example targets the parent ID, so it also affects variations of that product.

Compatibility

This is a cart-calculation hook, not a checkout-form display hook. Verify the result with your taxes, discounts, subscriptions, and checkout setup before using it in production.