Discounting Rules for Risky Assets

Stewart C. Myers and Richard S. Ruback

January 1993

Stewart C. Myers and Richard S. Ruback, Revised January 1993

This paper develops a new rule for calculating the discount rate to value risky projects. The rule works under any linear asset pricing model and any equilibrium theory of debt and taxes. If securities are priced by the standard capital asset pricing model, the discount rate is a weighted average of the after-tax Treasury rate and the expected rate of return on the market portfolio, where the weight on the market portfolio is the project beta. We prove that this discount rate gives the correct project value and explain why it works. We also recast the rule in certainty equivalent form, restate it for multifactor capital asset pricing or arbitrage pricing models, and derive implications for the valuation of real options.

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