變動所得課稅法制之省察與重構

Abstract

變動所得，在我國現行所得稅制下，對於納稅義務人帶來稅負升高之集遽效應，立法者乃透過所得稅法第14條第3項之基礎條文規定，予以處理。然而，關於變動所得之概念內涵及所得稅法第14條第3項之規範屬性，均存有重大爭議。又我國除了所得稅法第14條第3項規定外，是否有其他同樣屬於變動所得課稅法制之規定？在法無明文規定時，實務上又係如何處理？我國現行變動所得課稅法制，在立法論上有無可資改進的空間？應取向於何種制度設計模式？凡此，均屬我國租稅法制面對變動所得此一議題，亟需處理的重要問題。 本文透過我國文獻之回顧與省思，並與外國法制加以比較與思考，指出變動所得係指長期累積而一次大量實現之所得，並不以現行所得稅法第14條第3項規定之四類為限，其課稅規範應具有反映量能課稅原則之規範意涵。而在所得稅法第14條第3項規定外，我國另有其他針對各別變動所得而制定的課稅規範，實務上亦自行發展其他變動所得課稅機制，致使我國關於變動所得之課稅規範現況，呈現極為紛雜的現象。本文基於平等原則之思考，認為有作統一處理之必要；立法論上，並得以變動所得是否具有「可得回算性」之此一特徵，作不同立法上的處理，以試圖接近量能課稅原則的建制要求。

Under Taiwan’s current income tax system, variable income gives rise to a bunching effect in tax burdens for taxpayers. The legislature has addressed this issue through the foundational provision of Article 14, Paragraph 3 of the Income Tax Act. However, both the conceptual scope of variable income and the normative character of Article 14, Paragraph 3 remain subjects of significant controversy. Moreover, aside from this provision, it is unclear whether other statutory rules in Taiwan’s tax law framework similarly pertain to the taxation of variable income. In the absence of explicit legal provisions, how such income is handled in practice also warrants examination. These questions—whether Taiwan’s current legal framework for taxing variable income is adequate, whether it can be improved legislatively, and what model of regulatory design should be adopted—represent pressing issues that must be addressed within Taiwan’s tax law system. This article, through a review and reflection on domestic literature and a comparative analysis of foreign legal systems, argues that variable income refers to income that is accumulated over a long period and realized in a lump sum, and should not be limited to the four categories enumerated under Article 14, Paragraph 3 of the Income Tax Act. The taxation of such income should reflect the normative implications of the ability-to-pay principle. Beyond Article 14, Paragraph 3, Taiwan’s legal system contains other provisions targeting specific types of variable income, and in practice, additional mechanisms have evolved to address such income, resulting in a highly fragmented regulatory landscape. From the perspective of tax equity, this article contends that a unified approach is necessary. Legislatively, it proposes that the presence or absence of “recomputability”—i.e., the ability to retroactively allocate income across prior years—may serve as a meaningful criterion for differentiated regulatory treatment, in pursuit of a tax system more closely aligned with the ability-to-pay principle.