Spending Multiplier Calculator

Estimate how much total economic output an initial change in spending generates using the Keynesian expenditure multiplier k = 1 / (1 - MPC(1-t) + m), built from your marginal propensity to consume, marginal tax rate, and marginal propensity to import.

Quick Facts

Formula
k = 1 / (1 - MPC(1-t) + m)
MPC is the marginal propensity to consume, t the marginal tax rate, and m the marginal propensity to import.
Model
Keynesian expenditure (fiscal) multiplier
Assumes MPC, tax rate, and import rate stay constant as income changes.
Simple case
k = 1 / (1 - MPC)
The textbook closed-economy version, with no taxes or imports.

Your Results

Calculated
Spending multiplier
-
Change in output per $1 of initial spending
Total change in output
-
Initial spending × multiplier
Induced (multiplier) effect
-
Total output minus the initial spending itself
Simple multiplier (no leakage)
-
1 / (1 - MPC), ignoring taxes and imports

Ready

Enter the initial spending change, MPC, tax rate, and import rate, then press Calculate.

How the Spending Multiplier Calculator works

This tool answers a standard macroeconomics question: if spending in an economy rises (or falls) by some initial amount, how much does total output ultimately change once households re-spend part of that money? It uses the Keynesian expenditure multiplier, extended to account for taxes and imports, which are the two most common "leakages" that reduce how much of each new dollar keeps circulating.

The formula

For an initial change in spending ΔG, a marginal propensity to consume MPC (the share of each extra dollar of disposable income that households spend rather than save), a marginal tax rate t, and a marginal propensity to import m, the multiplier is:

k = 1 / (1 - MPC × (1 - t) + m)

The total change in output is ΔY = ΔG × k. Every round of spending, some income is saved, some is taxed away, and some is spent on imports instead of domestic goods — each of those is a leakage that shrinks the next round of re-spending, which is why the multiplier is always greater than 1 but bounded rather than infinite.

Worked example

Take a $10,000 increase in spending with an MPC of 0.75, a marginal tax rate of 20%, and a marginal propensity to import of 10%. The denominator is 1 - 0.75 × (1 - 0.20) + 0.10 = 1 - 0.60 + 0.10 = 0.50, so the multiplier is k = 1 / 0.50 = 2.00. Total output rises by $10,000 × 2.00 = $20,000, meaning the original $10,000 induces another $10,000 in follow-on spending. Without the tax and import leakages, the simple multiplier 1 / (1 - 0.75) = 4.00 would be twice as large — a reminder of how much leakages matter.

What moves the multiplier most

  • Marginal propensity to consume: a higher MPC means households save less of each new dollar, so more of it re-circulates and the multiplier rises quickly as MPC approaches 1.
  • Marginal tax rate: taxes remove income before it can be spent again, so a higher tax rate shrinks the effective MPC(1-t) term and lowers the multiplier.
  • Marginal propensity to import: spending on imported goods leaves the domestic economy instead of triggering another round of domestic spending, so a higher import rate also lowers the multiplier.

Limits of this model

This is the standard textbook formula, which assumes MPC, the tax rate, and the import rate are constant regardless of how large the spending change is or the state of the business cycle. It does not model crowding out (higher government borrowing pushing up interest rates and reducing private investment), a monetary policy response, supply-side capacity limits, or shifts in expectations. Real-world multiplier estimates vary with these factors, so treat this calculation as a transparent baseline rather than a forecast, and this page is for computation and education only, not personalized financial or policy advice.

Frequently Asked Questions

What formula does this spending multiplier calculator use?
It uses the Keynesian expenditure multiplier for an open economy with taxes: k = 1 / (1 - MPC(1-t) + m), where MPC is the marginal propensity to consume, t is the marginal tax rate, and m is the marginal propensity to import. The total change in output equals the initial change in spending multiplied by k.
What is the difference between the multiplier shown and the simple multiplier?
The simple (closed-economy) multiplier is 1 / (1 - MPC) and ignores taxes and imports. The full multiplier used for the main result also subtracts leakage to taxes and imports, so it is always less than or equal to the simple multiplier for the same MPC. The calculator reports both so you can see how much taxes and imports reduce the effect.
What happens if the marginal propensity to consume is very high?
As MPC approaches 1 (households spend nearly all of each extra dollar), the denominator of the multiplier shrinks and the multiplier grows rapidly, meaning small amounts of new spending produce large increases in total output. In practice very high MPC values are uncommon and the multiplier is bounded well above 1 once realistic tax and import rates are included.
Does this model account for real-world complications like crowding out?
No. This is the standard textbook Keynesian multiplier, which assumes MPC, the tax rate, and the import rate stay constant as income changes and does not model crowding out, monetary policy offsets, supply constraints, or changes in expectations. Empirical multiplier estimates from real economies vary and should be used alongside this simplified formula, not in place of it.

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