# Tax calculation
Tax calculation in the Salesforce Lightning app is segregated into two separate layers. The inner layer, the `DRB2B_CartTaxCalculations` class, contains both the API connector and messaging functionality.
Use the outer layer, `DRB2B_TaxCalculationService` class, as a global service that can be used as a stand-alone integration. This service has a `startCartProcessAsync`method which takes `CartId (id)`and `sfdc_checkout.IntegrationInfo` which returns a `ResponseModel`custom apex object.
After making the API call to Digital River, the service uses the checkout service to store the response in the `CartTax` object. The `DRB2B_TaxCalculationService` service is used in both synchronous and asynchronous checkout flows.
Refer to the following example to understand how to use tax calculation in an the asynchronous checkout context:
As an alternative to the previous example, you can call the tax calculation routine yourself. Refer to the following example to understand how the service can be called in a stand-alone use case:
The following table provides details on the input parameters used in tax calculations:
| Input variable name | Description |
| ------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| cartId |
Type: Id
Identifies the cart in the checkout session.
|
| jobInfo |
Type: sfdc\_checkout.IntegrationInfo
Used in cases of an asynchronous checkout process used to load exceptions and related messages into a session. This can be NULL when used as stand-alone process.
|
The following table provides information on the output parameters used in tax calculations:
| Variable name | Description |
| --------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| ResponseModel.status |
Type: String
Possible values:
“Error” – This is passed when an exception or validation error occurs because the tax calculation cannot completed.
“Success” – This is passed when tax calculation was success.
|
| ResponseModel.message |
Type: String
Provides the response string message passed on when there is an exception.
