최저한세 제도는 특정기업에 적용되는 조세감면의 종합적인 한도를 정하여 경제적 능력에 따른 최소한의 조세부담을 규정함으로써 기업들이 부담하는 유효세율이 비슷해지도록 조정하여 조세부담의 공평성을 확보하는 제도이다. 본 연구에서는 최저한세의 시행으로 인하여 전체적으로 또는 기업특성변수에 따라 조세부담의 공평성이 향상되었는지 여부와, 또 그 결과가 중소기업에 대한 최저한세율이 인하된 2004년을 전후하여 차이를 보이는지 여부를 검정하였다. 실질적으로 단일세율제도에 가까운 현행 법인세법 하에서 기업의 조세부담의 공평성의 정도를 측정하기 위해 유효세율의 변동계수와 부담할 세액의 잔차변동계수를 불평등도지수로 사용하였고, 표본기업으로 서울지역의 영리내국법인들 중에서 2001년 이후 매년 당기순이익을 보고한 법인들 중 무작위로 405개를 선정하였으며, 연구의 결과를 요약하면 다음과 같다. 첫째, 연구대상 기간인 2003년과 2004년에 모두 최저한세의 시행으로 전체적인 조세부담의 공평성이 향상되었다. 둘째, 2003년과 2004년에 모두 대기업의 조세부담의 공평성이 중소기업보다 더 향상되었는데, 예상과 다른 이러한 결과는 중소기업의 최저한세 납부가능성이 대기업보다 클 것이라는 전제가 달성되지 않았기 때문인 것으로 보인다. 셋째, 2003년과 2004년에 모두 1·2차산업 기업의 조세부담의 공평성이 3차산업 기업보다 더 향상되었다. 넷째, 2003년과 비교할 때 기본세율과 대기업의 최저한세율은 변하지 않았지만 중소기업의 최저한세율은 인하된 2004년에 중소기업의 최저한세 납부가능성은 대기업보다 상대적으로 더 낮아졌고, 중소기업의 조세부담의 공평성은 대기업보다 상대적으로 더 악화되었다. 선행연구의 성과와 비교했을 때 본 연구의 공헌은 다음과 같다. 첫째, 실증분석을 통하여 조세부담의 공평성의 정도는 최저한세 납부가능성에 비례함을 보였다. 둘째, 2003년과 2004년의 연도간 비교를 통해 법인세 기본세율과 최저한세율의 상대적인 변화에 따른 최저한세 납부가능성의 변화를 보였고, 이에 따른 조세부담의 공평성의 변화를 보였다.
Alternative minimum tax (AMT) is supposed to guarantee the corporate tax burden equity (`equity`hereafter), limiting the whole tax benefit of a firm and thus forcing the firm to pay the rock-bottom tax burden liability proportionate to its economic ability. We tested empirically whether the AMT actually improved the equity as a whole and in each segment of corporate groups, and whether the equity results might differ before and after 2004 when both basic corporate tax rate and the AMT rate for large firms stayed unchanged while the AMT rate for small-to-mid sized firms were lowered. Under the current corporate tax regime, virtually single-rate taxation, the equity can be measured by either how small the variation of tax burden rate is or how well the distribution of tax burden liability is proportionate to income. We used both the coefficient of variation (CV) of corporate tax burden rate and the coefficient of residual variation (CRV) of corporate tax burden liability to measure the equity. We estimated the regression line with no intercept in calculating to measure the equity. We estimated the regression line with no intercept in calculating the CRV to specifically emphasize the single-rate taxation property. We randomly selected 405 sample firms headquartered in Seoul which have reported positive annual net income consecutively since 2001. While the prior studies mainly analyzed the equity of individual income tax which has a significant progressive tax rate structure, this study focused on the corporate income tax which has a single tax rate structure and, thus, didn`t have to divide the sample firms into ability-based subgroups. We found following empirical results: First, the AMT improved the overall equity during the sample period, in 2003 and 2004. Second, the improvement of the equity among large firms were higher than that among small-to-mid sized firms in 2003 and 2004. The equity is construed as proportionate to taxpayer`s probability to pay AMT. We expect the contrary result since there are lots of tax benefit provisions in the current corporate income tax law in favor of small-to-mid sized firms and thus they are more likely to pay AMT. We presume that our finding is due to either the fact that the large firms, which have a high level of tax law knowledge, used the tax benefit provisions more aggressively or the fact that the small-to-mid sized firms in this study were not able to utilize many tax benefit provisions as they are located in a metropolitan Seoul area. Third, in 2003 and 2004, the AMT improved the equity among primary-and-secondary industry firms more than that among trinary industry firms, strengthening the single-rate taxation property more in the primary-and-secondary industry firms group. We expected the primary-and-secondary industry firms were more likely to pay AMT as there are more tax benefit provisions in favor of them. Our finding confirms the expectation. Last, the AMT worsened the equity of small-to-mid sized firm from 2003 to 2004 relatively more compared to that of large firms. We expected that small-to-mid sized firms were relatively less likely to pay AMT in 2004 than in 2003 since both basic corporate tax rate and the AMT rate for large firms stayed unchanged while the AMT rate for small-to-mid sized firms were lowered in 2004. Our finding confirms the expectation. Thins study is significant in that it verifies whether the AMT provision has achieved the intended economic function, using plentiful and timely sample firms data and analyzing the recent effect on the equity caused by the asymmetric change in the corporate tax rate scheme. Compared to prior studies, we showed that the equity is proportionate to the probability to pay AMT. We also showed that the asymmetric change in the corporate tax rate structure affects the probability to pay AMT, resulting in the shift of equity.
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