What is used to calculate the notional interest cost in the residual income equation?

The calculation of the notional interest cost in the residual income equation is based on the cost of capital and net assets. This approach reflects the opportunity cost of using funds in a particular investment, assuming that investors expect a return on their capital that is at least equal to the cost of capital.

By multiplying the cost of capital by net assets, the resulting figure represents the minimum return that the business needs to earn to satisfy its investors. If the actual returns exceed this notional interest cost, it indicates that the company is creating value over and above the investors' expectations. This is crucial for measuring whether a business unit is performing well enough to justify the resources invested in it.

Using total assets instead of net assets, as seen in other choices, does not adequately capture the return requirement on the equity invested, as total assets include liabilities as well. Therefore, focusing on net assets provides a clearer indicator of performance relating to the capital contributed by shareholders or owners.