This paper first documents the evolution of the cross-sectional income and consumption distribution in the US in the past 25 years. Using data from the Consumer Expenditure Survey we find that a rising income inequality has not been accompanied by a corresponding rise in consumption inequality. Over the period from 1972 to 1998 the standard deviation of the log of after-tax labor income has increased by 20% while the standard deviation of log consumption has increased less than 2%. Furthermore income inequality has increased both between and within education groups while consumption inequality has increased between education groups but mildly declined within groups. We then argue that these empirical findings are consistent with the hypothesis that an increase in income volatility has been an important cause of the increase in income inequality, but at the same time has lead to an endogenous development of credit markets, allowing households to better smooth their consumption against idiosyncratic income fluctuations. We develop a consumption model in which the sharing of income risk is limited by imperfect enforcement of credit contracts and in which the development of financial markets depends on the volatility of the individual income process. This model is shown to be quantitatively consistent with the joint evolution of income and consumption inequality in US, while other commonly used consumption models are not.

In this paper we quantitatively characterize the optimal capital and labor income tax in an overlapping generations model with idiosyncratic, uninsurable income shocks, where households also differ permanently with respect to their ability to generate income. The welfare criterion we employ is ex-ante (before ability is realized) expected (with respect to uninsurable productivity shocks) utility of a newborn in a stationary equilibrium. Embedded in this welfare criterion is a concern of the policy maker for insurance against idiosyncratic shocks and redistribution among agents of different abilities. Such insurance and redistribution can be achieved by progressive labor income taxes or taxation of capital income, or both. The policy maker has then to trade off these concerns against the standard distortions these taxes generate for the labor supply and capital accumulation decision. We find that in our model the optimal capital income tax rate is significantly positive. The optimal (marginal and average) tax rate on capital is 36%, in conjunction with a progressive labor income tax code that is, to a first approximation, a flat tax of 23% with a deduction that corresponds to about $6,000 (relative to an average income of households in the model of $35,000). We argue that the high optimal capital income tax is mainly driven by the life cycle structure of the model whereas the optimal progressivity of the labor income tax is due to the insurance and redistribution role of the income tax system.

We quantitatively characterize the optimal capital and labor income tax in an overlapping generations model with idiosyncratic, uninsurable income shocks and permanent productivity differences of households. The optimal capital income tax rate is significantly positive at 36 percent. The optimal progressive labor income tax is, roughly, a flat tax of 23 percent with a deduction of $7,200 (relative to average household income of $42,000). The high optimal capital income tax is mainly driven by the life-cycle structure of the model, whereas the optimal progressivity of the labor income tax is attributable to the insurance and redistribution role of the tax system. (JEL E13, H21, H24, H25)