To add the discount in opencart programmatically follow the following steps: 1. Open <projectFolder>/catalog/model/total/coupon.php 2. Add the code in the getTotal() function $discount_total=0; if($total>=0 && $total<=500){ $discount_total=$total*0.1; }else if($total>500 && $total<=1000){ $discount_total=$total*0.2; }else if($total>1000 && $total<=10000){ $discount_total=$total*0.3; } */ $total_data[] = array( 'code' => 'discount', 'title' => sprintf("My Special Discount"), 'value' => -$discount_total, 'sort_order' => 4 ); 3. Now add the products in the cart 4. Goto Cart page check your order info (See the sample screenshot)