Promotion Proration Logic

For order-based and total-fixed promotions, discounts are prorated across multiple products to spread the weight of the discount across the products. The proration also determines the amount a shopper is refunded when returning a discounted product.

Proration uses a step algorithm. Discounts are calculated based on the total price and total discount price. To avoid losing precision because of rounding, the discount amount and the ultimate cost of the products are recalculated after applying the promotion to each product. Each product receives a portion of the discount. The last product in the list receives the remainder of the discount. The amount of the discount applied to each product depends on the product's initial cost.


A cart has three items. SKU1 costs $13, SKU2 costs $13, and SKU3 costs $12, for a total of $38. The promotion offers all three items for $22, for a total discount of $16.

Product Original Cost Promotion Proration Discount Adjusted Price Remaining Discount Remaining Total Price
SKU1 13 (13 * - 16) / 38 -$5.47 $7.53 -$10.53 (16 - 5.47) $25 (38 - 13)
SKU2 13 (13 * - 10.53)/25 -$5.48 $7.52 -$5.05 (10.53 - 5.48) $12 (25 - 13)
SKU3 12 NA -$5.05 $6.95 0 0
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