The paper considers the issues of applying budget classification as an accounting tool necessary for separate accounting of income and expenses of commercial organizations. The budget classification can also be applied by commercial organizations for the purpose of internal control of the receipt and use of funds earned in the course of activities or subsidies and grants received from the state budget. The issues of external and internal financial control are relevant and are widely discussed by the professional community in terms of finding its effective mechanisms. The purpose of the study is to adapt a harmonized approach to the application of budget classification by economic entities of various groups: commercial organizations of the real sector, organizations of the budgetary sphere, non-profit organizations of the real and public sectors, as an instrument of external and internal control. The methodological basis of the study was the general scientific principles and methods of research: analysis and synthesis, logical linking, systematization. The proposed author's approach to the application of budget classification can be implemented both in the process of improving regulatory regulation and in the process of compiling external and internal reporting by economic entities. The main results obtained by the author allow us to improve the tools of internal control for commercial organizations of the real sector and non-profit organizations of the real and public sector. The classification of operations of the public administration sector is unified, as it reflects the economic content of the facts of economic life, and can be used for management accounting and budgeting by commercial organizations of the real sector, as well as for the control of targeted financing by non-profit organizations of the real and public sector. The harmonized codes of economic classification proposed in the work will make it possible to organize separate cost accounting, including when commercial organizations fulfill a state (defense) order.