Speedy Calculator

Spending Multiplier Calculator

Finance Updated October 25, 2026

Quick answer

The spending multiplier calculator works out the Keynesian spending multiplier from the marginal propensity to consume – with optional tax and import leakages – and the total change in GDP from a change in spending.

%
$
Simple spending multiplier
—
Multiplier with leakages
—
Change in GDP
$ —
Tax multiplier
—

Taxes and imports “leak” spending out of the domestic circular flow, so real-world multipliers are much smaller than the textbook 1 ÷ (1 − MPC) – often estimated at 0.5–2 depending on the policy and the state of the economy.

How to use the Spending Multiplier Calculator

  1. Marginal propensity to consume (MPC)
  2. Tax rate
  3. Marginal propensity to import
  4. Change in spending

Results update as you type, and every field accepts the units shown in its menu.

How it works

Enter the MPC, the tax rate, the marginal propensity to import and the change in spending.

Tips

  • Use real (inflation-adjusted) figures to compare across years.
  • Check whether data are seasonally adjusted.
  • Use the same currency and base year throughout.
  • Economic models simplify reality – treat results as illustrations, not forecasts.

Common mistakes to avoid

  • Mixing nominal and real values.
  • Comparing percentage changes with percentage-point changes.
  • Treating correlations as causes.

Inputs explained

Field What to enter
Marginal propensity to consume (MPC) A number
Tax rate In %
Marginal propensity to import A number
Change in spending Amount in your currency

What each result means

  • Simple spending multiplier = 1÷(1 – [Marginal propensity to consume (MPC)])
  • Multiplier with leakages = 1÷(1 – [Marginal propensity to consume (MPC)]×(1 – [Tax rate]÷100) + [Marginal propensity to import])
  • Change in GDP = [Change in spending]×[Multiplier with leakages]
  • Tax multiplier = 0 – [Marginal propensity to consume (MPC)]×[Multiplier with leakages]

Formula

Simple multiplier = 1 ÷ (1 − MPC)With leakages = 1 ÷ (1 − MPC × (1 − t) + MPI)Change in GDP = multiplier × change in spending

Worked example

Inputs — Marginal propensity to consume (MPC): 0.8; Tax rate: 0 %; Marginal propensity to import: 0; Change in spending: $100.
Results — Simple spending multiplier = 5; Multiplier with leakages = 5; Change in GDP = $500.00; Tax multiplier = -4.

Frequently asked questions

What is the spending multiplier?

How much GDP changes for each dollar of new spending.

How is it calculated?

1 ÷ (1 − MPC), reduced by taxes and imports.

What is the tax multiplier?

−MPC × spending multiplier; it's smaller than the spending multiplier.

What formula does the Spending Multiplier Calculator use?

Simple multiplier = 1 ÷ (1 − MPC).

Cite this calculator

Speedy Calculator. (2026). Spending Multiplier Calculator. Speedy Calculator. https://speedycalculator.com/calculators/finance/spending-multiplier/