By strengthening international cooperation and harmonizing the legal framework, entrepreneurs are increasingly doing business outside their home country and are in demand for an improving economic environment that would preserve profitability as much as possible. In order to attract foreign investments, countries are ready to provide as many benefits as possible in order to attract foreign capital and become bigger competitors on the European market, and the differences in legal frameworks and the way profits are taxed through tax planning can be used wisely by entrepreneurs to reduce tax liability and increase profitability. Although the idea of the internal single market of the European Union is based on the free movement of people and capital, differences in the tax system between member states prevent fair market competition and an even distribution of capital. In order to enable fairer market competition and prevent harmful tax evasion, the European Union is working on harmonizing the tax systems of member states in order to prevent the negative long-term consequences of mutual competition between states that primarily harms the well-being of their citizens. It comes to the conclusion that the current state of non-harmonized corporate tax rates in the European Union can be used wisely by entrepreneurs with knowledge of international law and tax planning methods in order to legally reduce the tax liability or perhaps even avoid it completely. What is being tried to prove is that the harmonized rate of corporate income tax would not significantly affect the profitability of companies, and companies could, with the help of other variables, influence the increase in profitability in addition to affecting the reduction of corporate tax.