The circular flow of income, injections and withdrawals, equilibrium real national output, and the multiplier effect.

What this dot point is asking

Edexcel wants you to explain the circular flow of income, identify injections and withdrawals, show how equilibrium output is reached where AD meets AS, and explain and calculate the multiplier.

The circular flow of income

The economy is in equilibrium when planned injections equal planned withdrawals: $I + G + X = S + T + M$. This is the same point as where AD meets AS. If injections exceed withdrawals, national income rises; if withdrawals exceed injections, it falls, until balance is restored.

Adjustment towards equilibrium

The adjustment is automatic. Suppose injections rise above withdrawals: firms see stocks fall and orders unmet, so they raise output and hire more workers. Higher output means higher household incomes, which raises withdrawals (more saving, tax and imports) until withdrawals climb back to match injections at a new, higher equilibrium income. The reverse happens after a fall in injections: unsold stock builds up, firms cut output, incomes fall and withdrawals shrink until balance returns at a lower income. This is why equilibrium output is not the same as full-employment output: an economy can settle at an equilibrium with a large output gap and high cyclical unemployment, which is the Keynesian case for active demand management.

The multiplier

For example, if the MPC is $0.8$, the multiplier is $\frac{1}{1 - 0.8} = 5$, so an extra $\pounds 1$bn of investment eventually raises national income by $\pounds 5$bn. The multiplier also works in reverse: a fall in an injection causes a magnified fall in income (the reverse multiplier).

The multiplier matters for fiscal policy: a high import propensity (a leaky economy) shrinks it, while crowding out and a near-full-employment economy reduce its real-output impact.

Injections, withdrawals and the output gap

The gap between equilibrium output and full-employment output is the output gap, and it shapes how an injection plays out. With a negative output gap (spare capacity, idle labour and capital), an injection mostly raises real output, so the real multiplier is large. With a positive output gap (the economy already at or above its trend capacity), the same injection mostly raises the price level, because firms cannot expand output, so the real multiplier is small and inflation results. This is why the timing of fiscal stimulus matters as much as its size: $\pounds 10$bn of extra spending in a deep recession does far more for real income than $\pounds 10$bn at the peak of a boom.

Evaluating the multiplier

The headline multiplier figure should always be qualified. Magnitude and the output gap: the multiplier is large only with spare capacity; the OBR and IMF estimate fiscal multipliers well above one in a deep recession but closer to zero near full employment, where extra demand is crowded out or inflated away. Time lags: the rounds of re-spending take months to play out, so the full effect of an injection is not felt in the quarter it occurs. Ceteris paribus: the simple formula assumes interest rates, the exchange rate and confidence hold still, yet a large fiscal injection can push up rates (crowding out private investment) or strengthen sterling (cutting net trade), both of which shrink the realised multiplier. A strong evaluation weighs these against the leakage size to judge how effective a given stimulus will be.

Examples in context

• Furlough multiplier (2020). UK fiscal support sustained household incomes and spending, with a relatively high multiplier because the alternative was a deep collapse in demand with much spare capacity. The scheme supported around 11.7 million jobs at its peak, keeping incomes circulating.
• Austerity (2010 to 2015). Critics, including the IMF in 2012, argued spending cuts had a larger negative multiplier than assumed because the economy had spare capacity, deepening and prolonging the slowdown.
• Import leakage. The UK's high marginal propensity to import dampens its multiplier compared with a more closed economy, because part of every extra pound spent flows abroad rather than to domestic firms.
• Infrastructure spending. Projects such as HS2 are defended partly on multiplier grounds, where construction wages are re-spent locally, though critics note the long build time delays the benefit and import content reduces the leakage-adjusted effect.
• Energy support and reverse multiplier (2022 to 2023). The Energy Price Guarantee injected support to households, sustaining spending that would otherwise have leaked into reduced consumption. The chain runs: capped bills protect real disposable income, households keep spending on other goods, firms keep revenue and staff, and the reverse multiplier (a magnified fall in income) is avoided. The evaluation point is that much of the support also flowed abroad through higher imported gas prices, so the domestic leakage was large and the multiplier on the policy lower than on equivalent domestic investment.
• North Sea oil and regional flows. Injections are not spread evenly across regions: spending concentrated in one area (such as construction in the South East) circulates locally first, so the regional multiplier can differ from the national one, which matters for "levelling up" policy that aims to raise income in lagging regions.

Try this

Q1. State two injections and two withdrawals from the circular flow. [4 marks]

• Cue. Injections: investment, government spending, exports. Withdrawals: saving, taxation, imports.

Q2. If the MPC is $0.75$, calculate the multiplier and the effect of a $\pounds 2$bn rise in government spending. [3 marks]

• Cue. Multiplier $= \frac{1}{1 - 0.75} = 4$; national income rises by $4 \times \pounds 2$bn $= \pounds 8$bn.