Modigliani and Miller Again Revisited: The Cost of Capital with Unequal Borrowing and Lending Rates

The financial literature asserts that financial managers must borrow at least to some degree if they are to optimise the value of their companies. This result has been described in the literature as ‘perhaps the single most important result in the theory of corporate finance obtained in the last 30 years’ (Copeland and Weston, 1988, p. 443). Based on US tax systems, the value added to a company by debt has been estimated as high as 35 to 50% of the debt's market value. More recently in this journal, Ashton (1989b) has argued that under the present UK tax system, the theoretical tax advantage afforded by debt should be estimated at no more than 13% of the debt's market value. The contribution of this paper is to draw attention to an aspect of borrowing that has largely escaped attention, but which nevertheless affects the above conclusions: namely, that the market spread between borrowing and lending constitutes a ‘cost’ for corporate borrowing. This paper demonstrates that in the context of the present UK tax system, this ‘cost’ of borrowing is sufficient to nullify entirely the formerly perceived financial tax benefits of corporate borrowing. We conclude that, at present, corporate borrowing could imply a net disadvantage for the valuation of a company's equity by about 6 or 7% of the debt's market value.