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  • John R. Graham,

    1. is Assistant Professor of Finance at Duke University's Fuqua School of Business.
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  • Michael L. Lemmon

    1. is Assistant Professor of Finance at Arizona State University's College of Business.
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      We thank Julie Collins for helping us identify some of the 1998 tax rules. Thanks also to Michael Annin, Don Chew, George Gallinger, John Ladrick, and Mitchell Petersen for helpful comments on a previous draft.


Taxes play an important but underemphasized role in the valuation of a company and its projects. For example, the authors estimate that the expected tax benefits from interest deductions by all publicly traded U.S. corporations were responsible for almost $1.4 trillion of their total market value of $12.7 trillion in 1991. In the case of RJR's 1989 leveraged buyout alone, the capitalized value of the interest tax shield amounted to several billion dollars (or about 25%) of the company's market value.

This article argues that, to maximize shareholder wealth, the corporate planning process should include a careful analysis of corporate tax incentives. Using several examples, the authors show how earnings variability and major provisions of the tax code interact to affect a company's expected marginal tax rate. After describing the complexities involved in properly calculating corporate tax rates, the article concludes by describing a simulation method the authors have developed to measure a company's effective marginal tax rate and, hence, its tax incentives to use more leverage (or some other means of reducing taxable income).

In furnishing a method for calculating marginal tax rates with greater accuracy, the authors also provide a clue to resolving the capital structure puzzle discussed in the roundtable at the head of this issue. In particular, their recent research corrects earlier studies in the finance literature by showing that when marginal tax rates are measured before financing (that is, based on income before interest expense is deducted), there is a positive relation between debt usage and tax rates.