근로소득공제율과 소득세율 변경의 구조적 누진성 영향

This paper analyzes the effects of change in the earned income deduction rates in 2014 and increase in the individual income tax rates from 2014 to 2018 in Korea on average rate progression(ARP) which is one of the measures of structural progressivity. ARP is measured by the rate of change in the average rate of tax and this paper analyses mathematically and empirically the ratio of ARPs, i.e. relative progressivity in ARPs between 2013 and 2018. For empirical analysis, gross income levels are selected arbitrarily in the range of 5,000,000 won and 1,000,000,000 won considering both the earned income deduction rates and the income tax rates. The mathematical and empirical results of the relative progressivity are as follows. According to the mathematical result using the tax function of Korean tax system under the simplified assumptions, the relative progressivity is determined by the relative ratio of the gradual amount deducted. The gradual amount deducted consists both income amount adjusted by the differences in the earned income deduction rates multiplied by the marginal tax rate and tax amount adjusted by the differences in the tax rates. According to the empirical result on the relative progressivity, the change in the earned income deduction rates has generally weakened progressivity, whereas the change in the income tax rates has strengthened progressivity, especially for high-income earners. This paper has value in that it defines the tax function containing variables of both the earned income deduction rates and the income tax rates and then evaluates structural progressivity by income levels both mathematically and empirically, whereas prior researches generally evaluate overall progressivity empirically.