Purpose. The aim of the article is the analysis of inequality of the population of Ukraine by sources of income. Methodology of research. A set of general scientific and specific methods of economic research was used in the course of the research, in particular, methods of theoretical generalizations: analysis, abstract and logical method (at substantiation of modern tendencies of inequality of the population of Ukraine on incomes); economic and statistical methods (in assessing the dynamics of inequality of the population of Ukraine in terms of monetary income); methods of mathematical statistics (when calculating the Gini index and the decomposition of income); methods of graphic display of the received results of research. Findings. The Gini index was calculated using the spline interpolation method to construct the Lorentz function. The Gini index is compared with known calculation methods, the description of the extended method of decomposition of the Gini index is carried out, and also this method is applied on statistical data of distribution of households of Ukraine on the level of monetary incomes. The influence of changes in sources of income on the general level of differentiation is analysed. According to the results of the study, the main factors influencing the level of income distribution and the possibility of reducing the level of stratification of the population of Ukraine were identified. Originality. It is proposed to use the spline interpolation method to construct the Lorentz function, which involves the calculation of the Gini index. The method of the Gini index decomposition identifies the sources of income that have the greatest impact on the growth of income inequality in Ukraine in the period 2014-2020. Practical value. The obtained results of the research are useful in the study of determining the reasons for the influence of certain factors on the level of income distribution and the possibility of reducing the level of stratification of the population of Ukraine. Key words: population inequality, Lorentz curve, Gini index, Gini index decomposition, spline interpolation.