Add suffix on price sale woocommerce

add_filter( 'woocommerce_get_price_suffix', 'custom_price_suffix', 999, 4 );
function custom_price_suffix( $html, $product, $price, $qty ){
    if ( $product->is_on_sale() ) {
        return  ' ' .  __('inc VAT', 'woocommerce');
    }
    return $html;
}

resources: stackoverflow