What Is the Marginal Propensity to Consume (MPC)? Formula and Examples

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The marginal propensity to consume (MPC) is the share of an additional dollar of income that a person, household or economy spends on goods and services instead of saving. It is written as a decimal between 0 and 1: an MPC of 0.8 means 80 cents of every extra dollar is spent and 20 cents is saved. The concept comes from Keynesian macroeconomics, where it determines how strongly a change in income ripples through total spending.

How the Marginal Propensity to Consume Works

The Formula

MPC = ΔC / ΔY

• ΔC is the change in consumption spending.
• ΔY is the change in income (in most applications, disposable income after taxes).

Graphically, MPC is the slope of the consumption function, a line that plots consumption on the vertical axis against income on the horizontal axis. A steeper line means a higher MPC: consumption rises more for each step up in income.

Interpreting the Number

• MPC = 0: all of the extra income is saved.
• MPC between 0 and 1: part is spent and part is saved. This is the normal case in theory.
• MPC = 1: every additional dollar is spent.
• MPC above 1: spending rises by more than income, which is possible only by drawing down savings or borrowing. It can happen for an individual for a period but is not sustainable.
• MPC below 0: spending would fall as income rises, which the standard model does not expect for normal consumption.

The Link to Saving

The counterpart is the marginal propensity to save (MPS = ΔS / ΔY). Because the model treats every extra dollar as either consumed or saved, MPC + MPS = 1. If MPC is 0.8, MPS must be 0.2.

Example of the Marginal Propensity to Consume

Hypothetical example. Suppose you receive a $500 bonus on top of your usual pay. You spend $400 on a new suit and put the remaining $100 into savings.

• MPC = $400 / $500 = 0.8
• MPS = $100 / $500 = 0.2
• Check: 0.8 + 0.2 = 1

Different behavior gives a different result: a person who received a $1,000 bonus, spent $100 and saved $900 would have an MPC of 0.1.

Why the Marginal Propensity to Consume Matters

The Keynesian Multiplier

In The General Theory of Employment, Interest and Money (1936), John Maynard Keynes made the propensity to consume central. When government spending or private investment rises, someone’s income rises. That person spends part of it, which becomes someone else’s income, and so on. Each round is smaller, because some of each dollar leaks into saving.

The size of the total effect depends on MPC. In the simplest model with no taxes or imports:

Multiplier = 1 / (1 − MPC) = 1 / MPS

Hypothetical example: with an MPC of 0.8, the multiplier is 1 / 0.2 = 5, so a $100 million increase in government spending would, in this model, raise total output, measured as gross domestic product, by up to $500 million. With an MPC of 0.5, the multiplier falls to 2 and the same spending raises output by $200 million.

MPC by Income Level

MPC is not constant across incomes. Households with low incomes tend to have a higher MPC, since much or all of any extra money goes to food, rent and other basic needs. As income rises and more needs are met, a larger share of each new dollar can be saved. This shapes policy design: a stimulus payment or tax cut aimed at lower-income households is expected to generate more immediate spending per dollar than one aimed at high earners.

Limitations of the Marginal Propensity to Consume

• It is not stable. MPC varies across people, income levels and time, so an economy-wide figure is an average that hides wide differences.
• Temporary vs. permanent income. Under Milton Friedman’s permanent income hypothesis, people base spending on expected long-run income, so a one-time windfall may be spent at a lower rate than a permanent raise of the same size. A measured MPC depends on what kind of income change produced it.
• The simple multiplier overstates effects. Taxes and imports are further leakages from each spending round, shrinking the multiplier below 1 / (1 − MPC).
• Other factors drive spending too. Interest rates, access to credit, household debt, wealth and confidence about the future all affect how much new income is spent, and the basic formula treats none of them.
• Measurement is difficult. Separating spending caused by an income change from spending that would have happened anyway requires careful data and assumptions.

MPC vs. Related Terms

MPC vs. average propensity to consume (APC). APC is total consumption divided by total income (C / Y), the share of all income spent. MPC is the share of additional income spent. A household spending $45,000 of a $50,000 income has an APC of 0.9, yet if a $1,000 raise leads to $600 of extra spending, its MPC is 0.6.

MPC as an acronym. In economics, MPC stands for marginal propensity to consume. In central banking it often refers to a Monetary Policy Committee, such as the Bank of England’s rate-setting body, which is unrelated to this concept.

FAQs

The Bottom Line

MPC matters to anyone studying macroeconomics or judging how stimulus payments, tax cuts or government spending will move the economy. A higher MPC means a larger spending multiplier, and lower-income households tend to spend more of each new dollar, so aid aimed at them is expected to produce more immediate spending. Treat the simple multiplier as an upper bound, since taxes, imports, credit, wealth and the type of income change all shape the real effect.