Desconto porcentagem

Tenho esse código

if (count($packageModel)) {

 $discountType = $package->getDiscountType();
 if ($discountType == Magestore_Membership_Model_Package_Discounttype::TYPE_FIXED)
 $result_price = $base_price - $productPrice;
 else if ($discountType == Magestore_Membership_Model_Package_Discounttype::TYPE_PERCENT)
 $result_price = ($base_price - $base_price * floatval($productPrice) / 100);
 else
 $result_price = $productPrice;
 }
 return $result_price;

Como posso dar 12% de desconto no resultado?