The main sources of social security in Iran are based on receiving insurance premiums and employment in the informal sector reduces the number of insurers, so, informal employment causes the loss of income sources of the Social Security Organization. Given the importance of the issue of lost financial resources for the Social Security Organization, in the present study, it has been tried to calculate the amount of informal employment in economic sectors during the years 2013 to 2019, estimate and analyze the lost financial resources due to informal employment. For this purpose, using households' expenditure and income micro data in the mentioned period, and utilization of social insurance indicators and legal minimum wage, informal employment was measured in terms of regions and economic sectors and its structure was analyzed. Then using the descriptive method and applying the concept of upgradeable informal employment, the amount of lost resources in major economic sectors and related sectors was calculated provincially and nationally. First, the results indicate that the share of informal employment to total employment has increased in the years under study. Also, among the 4 major economic sectors, the agricultural sector has the highest number of informal workers. Second, the lost financial resources due to informal employment have decreased during this period. In addition, among the four major economic sectors, the industries and mines section has the most lost social security resources.