Miles-Ezzell's Wacc Approach Yields Arbitrage

A simple counterexample shows the the widely used WACC approach to value leverage firms developed by Miles and Ezzell can create an arbitrage opportunity. The only consequence to be drawn is that their WACC approach cannot be applied under the circumstances assumed by Miles and Ezzell. We show how the WACC has to be modified in order to obtain proper results. We develop a theory in continuous as well as discrete time. In discrete time it turns out that with a further assumption on the cash flows of the firm formulas similar to Miles and Ezzell's results can be verified. This assumption requires that the increments of cash flows have to be uncorrelated. This is a much weaker assumption than independent increments which is used in models of random walk.