Tax Multiplier Calculator
Compute the Keynesian tax multiplier to estimate how a change in taxes ripples through the economy via consumer spending. Use it in macroeconomics courses or fiscal policy analysis to gauge the GDP impact of a tax change.
About this calculator
The tax multiplier is a macroeconomic concept from Keynesian theory that quantifies how much GDP changes for every one-unit change in taxes. The formula is: Tax Multiplier = −MPC / (1 − MPC), where MPC is the Marginal Propensity to Consume — the fraction of each additional dollar of disposable income that households spend rather than save. The negative sign reflects the inverse relationship: a tax increase reduces disposable income, causing consumers to spend less, which contracts GDP. The denominator (1 − MPC) equals the Marginal Propensity to Save (MPS). Because the initial spending cut triggers successive rounds of reduced income and spending across the economy, the final GDP impact is larger than the tax change itself — this is the multiplier effect. Importantly, the tax multiplier is always smaller in absolute value than the government spending multiplier (1 / (1 − MPC)) because a dollar of tax relief is partly saved, while a dollar of government spending enters the economy in full.
How to use
Suppose the MPC is 0.8, meaning households spend 80 cents of every additional dollar of income. Apply the formula: Tax Multiplier = −0.8 / (1 − 0.8) = −0.8 / 0.2 = −4. This means a $1 tax cut increases GDP by $4 (and a $1 tax increase reduces GDP by $4). So if the government cuts taxes by $50 billion and MPC = 0.8, the estimated GDP increase is $50 billion × 4 = $200 billion.
Frequently asked questions
Why is the tax multiplier negative in the Keynesian model?
The negative sign captures the inverse relationship between taxes and GDP. When taxes rise, households have less disposable income, so they consume less; reduced consumption means lower demand for goods and services, causing firms to produce less and GDP to fall. The reverse is true for tax cuts. The negative sign is a mathematical convention built into the formula to ensure that a positive tax increase correctly yields a negative change in GDP when you multiply the tax multiplier by the change in taxes. It is not a flaw but an intentional feature of the model.
What is the marginal propensity to consume and how does it affect the tax multiplier?
The Marginal Propensity to Consume (MPC) measures the share of each additional dollar of income that households choose to spend rather than save. It ranges from 0 (all income saved) to 1 (all income spent), with real-world estimates typically between 0.6 and 0.9. A higher MPC produces a larger tax multiplier in absolute value — if people spend most of a tax cut, each round of re-spending is bigger, amplifying the GDP effect. Conversely, if MPC is low (households save most of the tax cut), the multiplier is small. This is why fiscal stimulus is considered more effective when targeted at lower-income households, who tend to have higher MPCs.
How does the tax multiplier differ from the government spending multiplier?
The government spending multiplier is 1 / (1 − MPC), while the tax multiplier is −MPC / (1 − MPC). With an MPC of 0.8, the spending multiplier is 5 but the tax multiplier is only −4. The difference of 1 arises because every dollar of government spending directly injects a full dollar into the economy in the first round, whereas a dollar of tax reduction first passes through households, who save some fraction (1 − MPC) before spending the rest. This means direct government expenditure has a stronger initial impact on GDP than an equivalent tax cut — a critical consideration in designing fiscal stimulus packages during recessions.