Introduction . The predominant focus of management systems in the sphere of tour operators’ activity on retrospective financial accounting information does not allow tour operators to use the optimization planning function, which negatively affects their economic efficiency. Purpose . The aim of the article is to develop modern methodical approaches to improve the system of cost and profit planning at the enterprises of tour operators on the basis of the margin approach, which involves modeling the causal links between costs, income, profit on the one hand and the relevant factors that determine them – on the other. Results . In the article there is used a systematic approach to determine the place and role of the tour operator in the value chain of the tourism industry, the characteristics of the economic process of the tour operator and its economic relations with the external environment. To plan costs and profits there is used the apparatus of the theory of economic and mathematical modeling. Based on a systematic approach, the author's descriptive model of the tour operator's activity and its relations with counterparties in the market of resources and products is developed and proposed. This model provides classification of incoming resource flows of the tour operator into two types: resources purchased on the side of primary tourist services and resources that are necessary elements to perform various functions within the business process of the tour operator. According to the classification of resource flows, it is proposed to structure the costs of the tour operator into two groups: the cost of purchased primary travel services and conversion costs. In order to identify cost-generating factors, a comprehensive model of the economic process of the tour operator and the universal model of the main process of the enterprise are proposed. It is substantiated that the main economic process of a tour operator by the nature of the relationship between the flow of resources and the flow of products (services) can be defined as convergent. It is substantiated that the activity of the development of a complex of tourism product should be considered not as a separate function within the main process, but as an element of an independent innovative process of the tour operator. It is justified that resources are consumed not in the main economic process as a whole, but during the performance of individual functions within the main process. So the primary is causal link between cost-generating factors and consumed resources at the level of a particular function. For the sphere of tour operating activity, there are substantiated the criteria for identifying variable conversion costs: costs can be proportionally adapted to fluctuations in the volume of activity of a particular function and the volume of activity of the specified function behaves in direct proportion to the volume of the realized tourist services (quantity or cost of the realized tourist packages). It is substantiated that the «standard list» of variable conversion costs for the sphere of tour operators’ activity cannot be given, because variable costs are not an objective empirical phenomenon, and their behavior depends on the subjective management decision of an individual manager, which in turn is made within specific objective circumstances. According to W. Kilger's concept, it is proposed to determine 2 indicators of marginal cost: marginal cost for short-term decisions and marginal cost for long-term decisions, which is especially relevant in the allocation of costs for the situation of purchasing primary travel services on the basis of contracts with a guaranteed amount of capacity reservation. Originality . In the article there is proposed the methodical approach to formation of an indicator of normative marginal cost of a tourist product. Based on the concept of marginal profit, there is suggested the author's approach to planning of the costs and financial results of enterprises in the sphere tour operators’ activity. There is proposed a methodical approach to determine the break-even point of the tour operator based on the comparison of the planned marginal profit and the function of the total fixed and discretionary costs of the tour operator for the planned season. All abovementioned author's methodical approaches make up a scientific novelty, the use of which in the practice of enterprises in the sphere of tour operators’ activity allows to increase the efficiency of the management system and, accordingly, the profitability of enterprises. Conclusion . Thus, the use of the concept of the marginal profit in contrast to existing approaches allows to improve the quality of information support of the management system because within the proposed approach there is a possibility of more accurate modeling of cost and profit behavior at the enterprises of tour operators’ activity compared to the alternative concepts.