The optimal taxation of risky capital income: An elasticity rule

Should risky capital income be taxed like safe income or should tax rates be differentiated? The question is analyzed in a 2-assets model of portfolio choice. Flat tax rates are chosen in order to maximize the investor's expected utility from terminal wealth subject to an expected tax revenue constraint. If lump-sum taxes are not available, optimal tax rates are characterized by an elasticity rule: The relative change in the risk remuneration should be equal to the inverse of the product of two elasticities. One is the output elasticity of capital. The other is the demand elasticity for risky investments with respect to a revenue preserving tax variation.