Marginal Propensity to Consume Calculator - MPC

The marginal propensity to consume (MPC) calculator measures the share of an income change that is spent on consumption. Enter the change in income, ΔY, and the corresponding change in consumption, ΔC. The calculator reports MPC, marginal propensity to save (MPS), the simple Keynesian spending multiplier, and the tax multiplier. It is useful in introductory macroeconomics, policy discussions, household-behavior examples, and sensitivity analysis of consumption assumptions. The optional initial-income field provides context for the scenario but does not alter this marginal calculation. MPC is computed directly as ΔC ÷ ΔY. MPS is the unspent share, 1 − MPC. In the simple closed-economy model used here, the spending multiplier is 1 ÷ (1 − MPC), which is also 1 ÷ MPS. The tax multiplier is −MPC ÷ (1 − MPC). A positive income and positive consumption change produce the familiar result between zero and one when some incremental income is saved. The calculator also accepts matching negative changes, such as an income fall accompanied by reduced consumption. An MPC of 0.80 means that, in this observation, each additional dollar of income was associated with 80 cents of consumption and 20 cents of saving. A higher MPC produces a larger theoretical multiplier because a larger fraction of each new round of income is spent again. These multipliers are model outputs, not forecasts: real economies include imports, taxes, borrowing constraints, prices, interest rates, capacity limits, and changing expectations. Values at or beyond one make the simple multiplier unstable or unsuitable for interpretation. For sound analysis, use changes measured over the same period and for the same population. A one-time bonus, survey response, or aggregate national statistic can answer different questions, so record what ΔY and ΔC represent. Compare several plausible MPC values when evaluating fiscal scenarios and explain the assumptions alongside the result. This calculator performs the textbook arithmetic clearly, but it should complement rather than replace a full economic model or empirical study.