The marginal cost of capital is calculated as being the cost of the last dollar of capital raised. Generally we see that as more capital is raised, the marginal cost of capital rises . This happens due to the fact that marginal cost of capital generally is the weighted average of the cost of raising the last dollar of capital. Usually, we see that in raising extra capital, firms will try to stick to desired capital structure. Usually once sources are depleted they will have to issue more equity. Since the cost of issuing extra equity seems to be higher than other costs of financing, we see an increase in marginal cost of capital as the amounts of capital raised grow higher.