Optimal Fiscal Policy with Heterogeneous Agents and Capital: Overturning Chamley-Judd
What this paper finds — and why it matters
The Chamley-Judd result (1986) states that the optimal long-run capital income tax rate is zero in representative-agent models. This paper shows that introducing heterogeneous agents — specifically, agents with uninsurable idiosyncratic income risk who use precautionary saving — overturns this result. When agents differ in their wealth and income realizations, a capital income tax serves as a form of insurance that representative-agent models cannot provide. The paper derives a tractable analytical characterization of the optimal capital tax in an Aiyagari-type heterogeneous-agent model and finds that the optimal rate lies in the range of 10–30 percent at the steady state — strictly positive, in direct contradiction to Chamley-Judd. The magnitude of the optimal tax depends on the degree of idiosyncratic risk and the availability of alternative redistribution instruments: when other redistributive tools are limited, the optimal capital tax is higher.
Summary of a forthcoming paper, AI-assisted and human-reviewed. See the linked original for the authoritative claims and full conditions.
Q1. Why does heterogeneity overturn Chamley-Judd?
In representative-agent models, all agents hold the same capital stock, so a capital tax distorts intertemporal decisions identically and the Ramsey planner finds it optimal to zero out the distortion in the long run. With heterogeneous agents and uninsurable risk, the capital tax has an additional insurance role: taxing capital income and redistributing it reduces consumption variance across agents, generating welfare gains that outweigh the intertemporal distortion costs. The insurance benefit makes the optimal tax positive at the steady state because the tax-and-redistribute mechanism provides risk-sharing that incomplete markets cannot.
Q2. How tractable is the analytical result?
The paper derives closed-form expressions for the optimal tax rate as a function of the degree of idiosyncratic risk, the wealth distribution’s spread, and the available redistribution instruments, enabling comparative statics that go beyond what purely computational approaches provide. This tractability distinguishes the result from earlier numerical work that demonstrated positive optimal capital taxes without clear analytical structure.
Q3. What is the quantitative magnitude?
The optimal steady-state capital income tax is in the range of 10–30 percent, substantially above zero but well below confiscatory rates, in the paper’s benchmark calibration matched to U.S. income and wealth inequality. The range reflects the sensitivity to available redistribution instruments: the lower bound applies when the government has a rich set of redistribution tools, the upper bound when capital taxation is the only available instrument.
Key concepts
Chamley-Judd result : the proposition that the optimal long-run capital income tax is zero in representative-agent Ramsey taxation models; overturned in this paper once heterogeneous agents with uninsurable risk are introduced.
insurance role of capital taxation : the mechanism by which a capital income tax reduces consumption inequality in a heterogeneous-agent economy, generating welfare gains that outweigh the intertemporal distortion costs and making the optimal capital tax positive.