Fiscal policy changes aggregate demand (AD) through changes in government purchases and the tax system. Multipliers quantify how an initial policy change produces a larger (or smaller) final change in equilibrium real GDP.

Core idea: fiscal multipliers and total GDP impact

What a fiscal multiplier measures

In multiplier analysis, the goal is to translate a policy change (like $\Delta G$ or $\Delta T$) into the total change in equilibrium output, $\Delta Y$.

A Keynesian-cross (expenditure–output) diagram with the 45-degree line and planned aggregate expenditure, illustrating how equilibrium output is determined at the intersection. Shifts in autonomous spending move the planned-expenditure line, and the resulting change in equilibrium real GDP is larger than the initial vertical shift—graphically representing the multiplier. Source

The logic is that one person’s spending becomes another person’s income, creating additional rounds of spending.

A basic circular-flow diagram showing how spending on goods and services becomes income for households and firms, which then feeds back into further spending. This is the intuitive engine of the multiplier: repeated rounds of expenditure and income generation magnify an initial injection into aggregate demand. Source

Why the government spending multiplier is larger than the tax multiplier (syllabus claim)

A change in government spending enters AD directly: if the government buys 1 USD more of goods and services, initial spending rises by 1 USD.

A change in taxes affects AD indirectly: a 1 USD tax cut raises disposable income, but households typically spend only a fraction of that 1 USD and save the rest. Therefore, the initial boost to spending is smaller than 1 USD, making the overall multiplied effect smaller in absolute value.

The key behavioural parameter: MPC

Because the multiplier process depends on how much additional income is re-spent, MPC is central to calculating fiscal policy effects. A higher MPC means larger subsequent rounds of spending and a larger multiplier.

Multiplier formulas used for fiscal policy calculations

Government spending multiplier

This multiplier is positive: increases in $G$ raise equilibrium real GDP; decreases in $G$ lower it. The size depends on the share of extra income households spend each round.

Tax multiplier

The negative sign encodes direction: a tax increase reduces disposable income and consumption, lowering real GDP; a tax cut raises disposable income and consumption, increasing real GDP.

Comparing magnitudes: “larger” means absolute size

Spending multiplier vs tax multiplier (same MPC)

To compare “which is larger,” compare absolute values:

• $\left|\frac{1}{1-MPC}\right|$ versus $\left|\frac{MPC}{1-MPC}\right|$

• Since $0<MPC<1$, $1 > MPC$, so $\frac{1}{1-MPC} > \frac{MPC}{1-MPC}$

• Therefore, the government spending multiplier is larger than the tax multiplier in absolute size, matching the syllabus statement

Intuition in one line

• $G$ change: initial injection is the full $\Delta G$

• $T$ change: initial spending response is only $MPC \cdot (-\Delta T)$ because households save part of any tax change

Sign conventions and careful interpretation

Direction of GDP effects

When calculating $\Delta Y$, keep the policy sign with the change:

• Expansionary (raises GDP): $\Delta G>0$ or $\Delta T<0$

• Contractionary (lowers GDP): $\Delta G<0$ or $\Delta T>0$

What “taxes” means in these formulas

The standard tax multiplier expression assumes a lump-sum change (a fixed dollar change), not a change in tax rates with complicated feedback. On AP-style problems, the question typically specifies a dollar change in taxes and provides MPC (or enough information to infer it).

What to do when both $G$ and $T$ change

If a policy package includes both spending and taxes, compute each effect and add them:

• Total effect on equilibrium real GDP is the sum of the multiplied impacts from $\Delta G$ and $\Delta T$

• Track signs separately; they can reinforce or offset each other depending on whether both are expansionary, both contractionary, or mixed

Common pitfalls in multiplier calculations

• Using the tax multiplier formula for government spending (or vice versa)

• Forgetting the negative sign on the tax multiplier

• Comparing multipliers without using absolute value when the question asks “which is larger”

• Treating a tax cut as positive $\Delta T$ (by convention, a tax cut is $\Delta T<0$)