Add a discount programmatically to an Order in Woocommerce 3.2+

The only available feature to make a discount programmatically for an Order, is tricking the Fee API. For info, this trick is not recommended by woocommerce, but used by many people as there is not a discount feature in Woocommerce outside Coupons.

The following function will allow you to make a fixed discount of any amount or a percentage discount. The order need to exist (to be saved before).

The function code (For Woocommerce versions 3.2+):

/**
 * Add a discount to an Orders programmatically
 * (Using the FEE API - A negative fee)
 *
 * @since  3.2.0
 * @param  int     $order_id  The order ID. Required.
 * @param  string  $title  The label name for the discount. Required.
 * @param  mixed   $amount  Fixed amount (float) or percentage based on the subtotal. Required.
 * @param  string  $tax_class  The tax Class. '' by default. Optional.
 */
function wc_order_add_discount( $order_id, $title, $amount, $tax_class = '' ) {
    $order    = wc_get_order($order_id);
    $subtotal = $order->get_subtotal();
    $item     = new WC_Order_Item_Fee();

    if ( strpos($amount, '%') !== false ) {
        $percentage = (float) str_replace( array('%', ' '), array('', ''), $amount );
        $percentage = $percentage > 100 ? -100 : -$percentage;
        $discount   = $percentage * $subtotal / 100;
    } else {
        $discount = (float) str_replace( ' ', '', $amount );
        $discount = $discount > $subtotal ? -$subtotal : -$discount;
    }

    $item->set_tax_class( $tax_class );
    $item->set_name( $title );
    $item->set_amount( $discount );
    $item->set_total( $discount );

    if ( '0' !== $item->get_tax_class() && 'taxable' === $item->get_tax_status() && wc_tax_enabled() ) {
        $tax_for   = array(
            'country'   => $order->get_shipping_country(),
            'state'     => $order->get_shipping_state(),
            'postcode'  => $order->get_shipping_postcode(),
            'city'      => $order->get_shipping_city(),
            'tax_class' => $item->get_tax_class(),
        );
        $tax_rates = WC_Tax::find_rates( $tax_for );
        $taxes     = WC_Tax::calc_tax( $item->get_total(), $tax_rates, false );
        print_pr($taxes);

        if ( method_exists( $item, 'get_subtotal' ) ) {
            $subtotal_taxes = WC_Tax::calc_tax( $item->get_subtotal(), $tax_rates, false );
            $item->set_taxes( array( 'total' => $taxes, 'subtotal' => $subtotal_taxes ) );
            $item->set_total_tax( array_sum($taxes) );
        } else {
            $item->set_taxes( array( 'total' => $taxes ) );
            $item->set_total_tax( array_sum($taxes) );
        }
        $has_taxes = true;
    } else {
        $item->set_taxes( false );
        $has_taxes = false;
    }
    $item->save();

    $order->add_item( $item );
    $order->calculate_totals( $has_taxes );
    $order->save();
}

Code goes in function.php file of your active child theme (active theme). Tested and works.

---

USAGE Examples:

1) Fixed discount of $12 (with a dynamic $order_id):

wc_order_add_discount( $order_id, __("Fixed discount"), 12 );

2) Percentage discount of 5% (with a dynamic $order_id):

wc_order_add_discount( $order_id, __("Discount (5%)"), '5%' );

The amount (or the percentage) can be also a dynamic variable…

Actually you can just make hook before calculate tax etc, get subtotal, apply discount, done :) It automatically apply for Order message etc, it is visible also in backend in proper way. Even after remove hook, info about discount stay in order information.

// Hook before calculate fees
add_action('woocommerce_cart_calculate_fees' , 'add_user_discounts');
/**
 * Add custom fee if more than three article
 * @param WC_Cart $cart
 */
function add_user_discounts( WC_Cart $cart ){
    //any of your rules
    // Calculate the amount to reduce
    $discount = $cart->get_subtotal() * 0.5;

    $cart->add_fee( 'Test discount 50%', -$discount);
}