The purpose of this paper is to develop a novel calculation scheme for the costs of distribution per shipment according to a cost-by-cause principle. We propose to estimate the full costs of distribution routes excluding and including a new consignor. Then, we estimate the marginal costs per shipment and per consignor. The contributions of this paper are (1) a comprehensive list of drivers of Economies of Integration and (2) a calculation scheme, how to estimate true marginal cost of new consignors. Practitioners may deploy the method and insights of this paper for tariff design, negotiations, consignor acquisition, and also demarketing.