The article provides a definition of the shadow economy from the standpoint of institutional economic theory as an informal institution, as well as a legal category in accordance with domestic legislation. The dialectical unity and opposite of the shadow economy as an informal institution and a formal institution, which is subject to official assessments by state administration bodies, is determined. The phasing of the functioning of the shadow economy in Ukraine during 2010–2021 was carried out. The polynomial trends of its integral level at two selected stages (before 2014 and after) were formalized. It is shown that the general estimate of the shading level is obtained as a result of the integration of its estimates by four methods: population expenditure – retail turnover; electric; unprofitability of enterprises; monetary Quantitative estimates of the general and partial levels of shadowing of the economy are calculated: higher indicators are given by the monetary method and the population's expenses – turnover, lower – by electricity and unprofitable enterprises. Electrical and monetary methods are most closely related to the integral level. The ranking of methods for assessing the levels of the shadow economy was carried out according to the increase in the variability of their annual results based on the standard deviation: monetary, integral, unprofitability of enterprises, electric, population expenditure – retail turnover. The characteristics of individual methods of calculating the levels of shadowing of the economy and methods of integration in terms of content, order of calculation, advantages and disadvantages have been performed. It is shown that the integral assessment is determined as the sum of weighted average estimates of the level of the shadow economy by four methods based on the establishment of weighting factors taking into account the stability of estimates by the corresponding method for previous years, however, the flaws of the calculations are the failure to take into account the density of the correlation relationship between the levels of shadowing of the economy determined by different methods. Additional restrictions on the use of certain partial methods of measuring the shadowing of the economy, which reduce their information capacity in the conditions of martial law, have been determined. The greater rationality of using the monetary method in modern conditions has been proven. The main tools for reducing the level of the shadow economy in Ukraine are proposed: legalization of labor relations and, in general, economic activity in the country; restructuring of the money supply at the expense of the non-cash component; the spread of the use of the electronic payment system, primarily by subjects of small and micro-enterprises.