**Extended price** – Calculates the price including order-level discount amount (spread over all line items in the shipment) _and_ any line item discount amount.
**Discounted price** – Only calculates the price with the "line item discount amount," that is, the discount for a specific line item.
**Line item price** – Calculates the line item price, which includes a line item's extended price and discounted price.
**Sales tax** – Calculates a line item's sales tax.
**Sales tax** – Calculates line items' sales tax.

## Change the default calculation
By inheriting from the default implementation of the interface, DefaultLineItemCalculator, you can override the extended price and sales tax calculations. To change the calculation of a line item's extended price, override the CalculateExtendedPrice method. To change the calculation of line item's sales tax, override the CalculateSalesTax method.
## Change the default validation
The default implementation validates that the extended price and sales tax are not negative after the calculation. To change the behavior, override the ValidateExtendedPrice and ValidateSalesTax methods.