The purpose of this paper is to answer the question whether, despite the differentiation of the corporate income tax in the European Union, there are similarity patterns allowing for the harmonization of the bases of this tax. The analysed CIT static data both quantitative and qualitative concerns the years 2018 and 2020. The method of hierarchical cluster analysis allowed a grouping of EU countries according to their similarities. It also indicated the greatest tax differences between EU member states. In turn the affinity analysis made it possible to distinguish groups of countries which are similar in terms of CIT with the simultaneous identification of a pattern. Results show that despite significant differences in tax rates some EU states show convergence in tax bases. The geographical criterion still plays an important role in determining CIT structure and tax incentives are one of the tools that may be used in the approximation of the bases.