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Keynesian Spending Multiplier Calculator

Quantifies the total change in aggregate output resulting from an initial change in autonomous spending, where MPC is the marginal propensity to consume.

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Spending Multiplier

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Overview

The multiplier effect demonstrates how an initial injection of spending into an economy leads to a larger final increase in national income. This occurs because each dollar spent by one individual becomes income for another, who then spends a portion of that income again based on their marginal propensity to consume. As this cycle repeats, the cumulative effect on aggregate demand exceeds the size of the original stimulus.

Symbols

Variables

M = Spending Multiplier, M = Spending Multiplier

Spending Multiplier
Variable
Spending Multiplier
Variable

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When To Use

When to use: Use this when calculating the impact of fiscal policy, such as changes in government spending or investment, on total equilibrium GDP.

Why it matters: It explains why government stimulus packages can generate economic growth significantly larger than the initial cost to the treasury, provided there is spare capacity in the economy.

Avoid these traps

Common Mistakes

  • Confusing MPC (Marginal Propensity to Consume) with APC (Average Propensity to Consume).
  • Forgetting that the multiplier effect requires time to propagate through the economy.

One free problem

Practice Problem

If the Marginal Propensity to Consume (MPC) is 0.5, what is the value of the spending multiplier?

Spending Multiplier0.5

Solve for:

Hint: Calculate 1 divided by (1 - 0.5).

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. Keynes, J. M. (1936). The General Theory of Employment, Interest, and Money.
  2. Samuelson, P. A., & Nordhaus, W. D. (2010). Economics.
  3. Mankiw, N. G. (2020). Principles of Economics.