Expanding Modigliani and Miller [1958, 1963], we show that the theoretical
association between leverage and the cost of equity capital is decreasing in the corporate
tax benefit from debt and increasing in the personal tax disadvantage of debt. Using
various estimates for the implied cost of equity, we investigate the effects of corporate
and personal taxes on the association between financial leverage and the cost of equity.
We find that simulated corporate marginal tax rates before financing consistently explain
the association between leverage and the cost of equity. Although the results are sensitive
to the cost of equity and leverage estimates used, we interpret the overall evidence to be
consistent with the prediction that the corporate tax benefit reduces the leverage related
risk premium demanded by equity holders.