The Companies management accounting systems are essential tools to produce valuable information for decision makers. In recent years the ABC (Activity Based Costing) has been a very studied costing system. It improves the internal controls and provides greater precision to the necessities of high efficiency companies. In this context, the present study intends to apply the ABC through a Mathematical Practical Approach for Complex Organizational Structures where exists interactions of cost transferences between activities produced by its Internal Departments. To test the approaching adequacy in these organizations, it was done a Case Study in a Insurance Company with a Microsoft Excel simulation. As a result it was measured the costs of the Insurance Company internal activities with exactness and precision. Also, it was studied ways to establish the optimum relation between necessary controls to the system and the costs that they generate for the Company, through some assembling flexibilities.