Macroeconomic models routinely abstract simultaneously from two features of the US federal tax code: the joint taxation of ordinary capital and labor income and the special taxation of preferential capital income. In this article, we argue that this abstraction omits a “portfolio-effect” mechanism where endogenous changes to the ordinary-preferential composition of households’ capital income influence individuals’ optimal labor and saving decisions through its impact on their effective marginal tax rates. We demonstrate the quantitative importance of this tax detail by simulating provisions from the recently enacted “Tax Cuts and Jobs Act” using a heterogeneous-agent overlapping generations framework calibrated to the US economy. Our findings imply that accounting for the detailed taxation of labor and capital income should be considered an important modeling feature for tax policy analysis.

宏观经济模型通常同时从美国联邦税法的两个特征中抽象出来：普通资本和劳动收入的联合征税和优惠资本收入的特别征税。在本文中，我们认为这种抽象忽略了“投资组合效应”机制，即家庭资本收入的普通优惠构成的内生变化通过其对有效边际税率的影响来影响个人的最优劳动和储蓄决策。我们通过使用根据美国经济校准的异质代理重叠世代框架模拟最近颁布的“减税和就业法案”中的规定，证明了这一税收细节的定量重要性。