This equation is pretty simple and incredible useful for management because it looks at one of a department’s key components of success: its required rate of return. This component helps management evaluate whether the department is making enough money to maintain, close, or expand its operation. It’s essentially an opportunity costmeasurement based on the trade off of investing in capital in one department over the other. For instance, if management can invest company revenues in department A and earn a 15% return, department B would have to make at least 15% in order for the management to consider the investment. If department B doesn’t meet minimum 15% return rate, it might be shut down or redirected.
Residual income is calculated as net income less a charge for the cost of capital. The charge is known as the equity charge and is calculated as the value of equity capital multiplied by the cost of equity or the required rate of return on equity. Given the opportunity cost of equity, a company can have positive net income but negative residual income.