The effect of corporate taxes on the market value of a levered firm continues to be a central issue in recent contributions in finance theory (e.g., Miller 1977; DeAngelo and Masulis 1980; Kim 1982; Modigliani 1982). In these and other studies (e.g., Krause and Litzenberger 1973; Scott 1976; Brennan and Schwartz 1978; Kim 1978), the relationship between market value and capital structure is established by formulating a tax subsidy function that specifies the partial effect of debt on the expected tax savings at the corporate level under the existing U.S. tax code. A working assumption in most of these studies is that both principal and interest are tax deductible. This assumption is made in the spirit of the original Modigliani and Miller (1963) formulation in which debt is taken to be perpetual and riskless. Indeed, it is well known that the tax shield provided by the deduction of principal in a singleperiod framework has the same value as the tax shield from interest deductions in the case of perpetual and riskless debt. Under this assumption, it is shown that in the absence of non-debtThis paper examines the relationship between leverage and the value of the firm, when non-debt-related tax shields are available and the corporate tax is levied as an income tax. In a previous paper, De Angelo and Masulis argue that, in the presence of nondebt-related tax shields, the relationship between debt and firm value is concave, resulting in an interior optimal capital structure when there is a tax-induced differential in the cost of corporate debt. Their result derives from the fact that they assume the payment of debt principal and non-debt-related depreciation charges are deductible. However, the former deduction is consistent with a wealth tax, while the latter is consistent only with an income tax. We show that if the interest alone is deductible, the debt-firm value function is convex, resulting in corner solutions to the capital structure problem. * The authors wish to thank Richard Castanias, Richard Green, Lemma Senbet, and especially an anonymous referee for helpful comments, and Richard Green and Robert Dammon for computational assistance.
Read full abstract