Wighted Average Cost of Capital - WACC A calculation of a firm's cost of capital in which each category of capital is proportionately weighted. All capital sources - common stock, preferred stock, bonds and any other long-term debt - are included in a WACC calculation. [Source: Investopedia. See full entry for the formula and an explanation of its significance. See also: "Investors Need a Good WACC," by Ben McClure, for an article on how investors can us it for valuation.}