This document discusses the cost of capital and how firms calculate it. It defines the cost of capital as the rate of return a firm must earn on investments to maintain its stock price. A firm needs to calculate its weighted average cost of capital (WACC) to properly evaluate investment opportunities. The WACC takes into account the different costs of a firm's sources of capital, such as debt and equity, weighted by their proportions in the firm's target capital structure. The document outlines how to calculate the costs of different sources of capital and how to determine the WACC.