Figure11-2The Individual Consumption Function The consumption function relates a household’s current disposable income to its consumer spending. The vertical intercept, ac, is individual household autonomous consumer spending: the amount of a household’s consumer spending if its current disposable income is zero. The slope of the consumption function line, cf, is the marginal propensity to consume, or MPC; that is, for every additional $1 of current disposable income, MPC × $1 is spent.