This paper investigates optimal capital taxation in an innovation-driven growth model. We examine how the optimal capital tax rate varies with externalities associated with R&D and innovation. Our results show that the optimal capital tax rate is higher when (i) the “stepping on toes effect” is smaller, (ii) the “standing on shoulders effect” is stronger, or (iii) the extent of creative destruction is smaller. The optimal capital tax rate is more likely to be positive when there is underinvestment in R&D. Moreover, the optimal capital tax rate and the monopolistic markup exhibit an inverted-U relationship. By calibrating our model to the US economy, we find that the optimal capital tax rate is positive, at a rate of around 6.6%. Finally, we consider a number of extensions and find that the result of a positive optimal capital tax is robust.

A known result holds that capital taxes should be high in the short run and low or zero in the long-run steady state. This paper studies the dynamics of optimal capital taxation during the transition, when a high rate is no longer optimal but the economy is still in flux. The main result is that capital should be taxed whenever the sum of the elasticities of marginal utility with respect to consumption and labor supply are rising and subsidized whenever this sum is falling. If the utility function displays increasing relative risk aversion, this paradoxically implies that capital should be taxed when the capital stock is below the modified golden-rule level and subsidized whenever it exceeds this level. Thus, savings incentives sometimes can be more desirable when the capital stock is large than when it is small.