Marginal Benefits Additional benefits; the benefits connected with consuming an additional unit of a good or undertaking one more unit of an activity. Marginal Cost (MC) The change in total cost that results from a change in output: MC 5 ΔTC/ΔQ. Marginal Costs Additional costs; the costs connected with consuming an additional unit of a good or undertaking one more unit of an activity. Marginal Factor Cost (MFC) The additional cost incurred by employing an additional factor unit. Marginal (Income) Tax RateThe change in a person’s tax payment divided by the change in taxable income: DTax payment 4 DTaxable income. Marginal Physical Product (MPP) The change in output that results from changing the variable input by one unit, holding all other inputs fixed. Marginal Productivity TheoryFirms in competitive or perfect product and factor markets pay factors their marginal revenue products. Marginal Propensity to Consume (MPC) The ratio of the change in consumption to the change in disposable income: MPC 5 ΔC/ΔY d . Marginal Propensity to Save (MPS) The ratio of the change in saving to the change in disposable income: MPS 5 ΔS/ΔYd.