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 feesadd_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);}