The standard modeling practice in corporate finance has been to assume a linear tax schedule. This paper extends the structural contingent-claim model of corporate finance to incorporate a more realistic convex tax schedule. It is shown that tax convexity raises the optimal default boundary and thus increases the likelihood of default, and also reduces the optimal leverage ratio. While the former effect seems insignificant in general, the effect of tax convexity on the optimal leverage ratio can be quantitatively significant. We conclude that tax convexity should not be ignored in corporate financing decisions, and theoretical models should use a convex tax schedule instead of a linear one. Thus, the short answer to the question in the title is “No”.

This paper provides a theoretical derivation of commodity beta (stock price sensitivity to commodity price) using a contingent-claim model. The model incorporates operating leverage, financial leverage, costly financial distress, and mean reverting commodity prices; and highlights the important role played by the speed of reversion of the commodity price. It is used to identify theoretically the main determinants of commodity beta. Commodity beta is predicted to be an increasing function of the operating and financial leverage of the firm, and a decreasing function of the company’s tax rate and the level, volatility and speed of reversion of the commodity price. Empirical tests with a sample of gold mining firms provide support for these predictions, particularly the new implications of the model (the effect of the commodity price’s speed of reversion and the company’s tax rate).