所得稅單一稅率制(The Flat Tax) 主張取消累進課徵改採單一比例稅率,刪減租稅優惠改行單一個人免稅額,有助於稅制簡化、公平與效率, 故而受到全球關注。 台灣自2010年起, 營所稅已調整為17%單一稅率; 但綜所稅仍採累進課徵並給予多種減免, 顯得複雜且不公平。 本文旨在從稅負分配公平觀點, 藉由我國2004年所得稅申報核定資料,分析綜所稅改採單一稅率制的可行性。 實證主要發現:(1) 給予較高單一免稅額, 有助於稅負公平分配; 採比例稅率課徵,會產生稅負累退性。 (2) 就整體單一稅率制言, 具有相對較高之免稅額與稅率的制度,比相對較低免稅額與稅率者具租稅公平性。 (3)在一定的條件下, 台灣若將綜所稅改為20%單一稅率與每人單一免稅額34萬元,應能有助於所得公平分配並簡化稅政。

A flat tax system is a system with a single proportional tax rate, instead of
a system of progressive tax rates. It is a tax system with a simple personal
allowance, instead of a system with various tax preferences. In Taiwan, cor-
porate income tax is based on the adoption of a 17% single tax rate, but
individual income tax has remained progressive and is characterized by var-
ious types of tax relief, which have made the current system appear both
complicated and unfair. We thus analyze the feasibility of adopting a flat
tax system in Taiwan to replace the current system in order to create a fairer
and more simple tax system. This paper derives several results. Firstly, the
higher the allowance in a flat tax system, the fairer is the tax system. In
addition, a proportional tax system results in regressive taxes. Secondly, as
for the introduction of a flat tax system, a system with a relatively high tax
rate and a higher allowance will be fairer than a system with a relatively low
tax rate and a lower allowance. Thirdly, if Taiwan adopts the flat tax system
with a single tax rate of 20% and a single allowance of NT$340,000, it can
promote tax equity and simplify the tax administration.