The bank leverage response to tax shield changes

Does the preferential tax treatment of debt over equity cause banks to increase their leverage? We construct a novel dataset tracing the evolution of the debt tax shield for banks in advanced economies from 1870 to 2020. Exploiting variation from nearly all changes in banking-sector tax shields since the nineteenth century, we show that a 1 percentage point increase in the tax shield reduces bank capital ratios by 0.25-0.8 percentage points. Our estimates suggest that the tax advantage of debt was an important driver of the rise in bank leverage during the twentieth century.