When creating promotions, consider the effects of tax calculations.
Tax rates are determined as follows:
| Promotion Class | Tax |
|---|---|
| Product |
Uses the tax rate of the related product line item. For example, if a product line item has a 5% tax rate, the same tax rate is used for the price adjustment. |
| Order |
Calculates a mixed tax rate from all product line items in the cart. For example, the merchandise initial price is $105 and the merchandise-discounted price is $100. The tax rate set for all order-level price adjustments is (105 / 100) - 1 = 5%. |
| Shipping |
Uses the tax rate of the standard shipping line item in the shipment. For example, if a tax rate of 3% is set for the standard shipping line item, the same tax rate is used for the shipping price adjustment. |
If you need an alternative way to calculate tax for line items in an order, for example, your back-end systems can't handle order-level discounts, see Line Item Tax Basis.
- Line Item Tax Basis
Configure an alternative tax calculation for line items in an order with the B2C Commerce APIs (LineItem.updateTax ()) and Business Manager. This feature can be useful if your back-end systems can only handle product-level discounts but a line item requires you to prorate tax across an order. - Unit Level Rounding
If you prorate tax across an order, each line item has values for the single unit base price and the line item totals for gross, net, and tax. The single unit net price isn't calculated or stored. All rounding is done at the line level, which can cause rounding discrepancies. If your B2C Commerce site experiences these discrepancies, use unit-level rounding. - Prorating Promotions
Promotion discounts aren't prorated for each line item during the actual shopping process. However, B2C Commerce provides an API that calculates the prorated values in-memory and returns them to the caller upon request. Prorated price information is typically used to integrate with back-end order management and accounting systems that require all discounts to be itemized. - Promotion Proration Logic
Without proration, the promotion is calculated once at the end. With proration, the promotion is calculated proportionately for each line item. Proration helps when processing completed B2C Commerce orders, such as a product return.