Introduction to the circular flow of income

The circular flow of income shows income flowing between households and firms: households supply factors of production and receive incomes, which they spend on firms' output, generating revenue that firms pay out again as incomes. In a realistic open economy with a government, not all income stays in this flow — there are leakages and injections.

Leakages (withdrawals) are income that leaves the flow: savings (S) (income not spent), taxes (T) (income taken by the government), and imports (M) (spending that goes to foreign firms). Together they reduce the income passed on within the domestic economy.

Injections are spending that enters the flow from outside household consumption: investment (I) (firms' spending on capital), government spending (G), and exports (X) (foreign spending on domestic output). Together they add to the income circulating in the economy.

The level of national income depends on the balance between the two. If injections equal leakages (I + G + X = S + T + M), the amount entering equals the amount leaving, so national income is in equilibrium and stable. If injections exceed leakages, more money enters than leaves, so firms earn more revenue, pay more incomes and the circular flow expands — national income rises (raising output and employment). If leakages exceed injections, the flow contracts and national income falls.

Therefore changes in any injection or leakage — for example a rise in exports or government spending, or a fall in saving — change the level of national income by altering the balance between money entering and leaving the circular flow.

The three changes pull the circular flow in different directions.

Falling exports reduce an injection (X), so less foreign money enters the flow — this tends to lower national income.

Higher household saving increases a leakage (S), so more income is withdrawn rather than spent on domestic output — again tending to lower national income.

Higher government spending on infrastructure increases an injection (G), so more money enters the flow — tending to raise national income.

The net effect depends on the relative sizes of these changes. Two forces (lower exports and higher saving) reduce the flow, while one (higher government spending) increases it. If the fall in exports plus the rise in saving together outweigh the rise in government spending, then leakages exceed injections and national income falls (likely in a recession). The government's higher spending is a deliberate attempt to offset the contraction, but on its own it may not be enough to prevent a fall in national income.

Government spending (G) is an injection into the circular flow, so on the face of it raising G should increase national income.

The case that it raises national income. An increase in G directly raises injections. If leakages are unchanged, injections now exceed leakages, so more money enters the flow than leaves it: firms receive more revenue, pay more incomes to households, who spend more, and the circular flow expands. National income rises, usually accompanied by higher output and employment. This is the basis of expansionary fiscal policy, and is especially effective in a recession when there is spare capacity to meet the extra demand.

Reasons it may not always raise national income.

• Crowding out / financing. If the spending is financed by higher taxes (T), that raises a leakage, partly offsetting the injection; if financed by borrowing, it may push up interest rates and reduce private investment (I) — another injection — limiting the rise.
• Leakages elsewhere. If much of the extra income is saved or spent on imports, the boost to domestic income is smaller (more leaks out).
• Supply constraints. If the economy is already at or near full capacity, the extra spending mainly raises the price level (inflation) rather than real output, so real national income rises little (an AD/AS point).
• Wasteful spending. If G is spent inefficiently, it may add little productive value.

Judgement. An increase in government spending tends to raise national income because it is an injection, and it is most effective when the economy has spare capacity, the spending is not fully offset by higher taxes or reduced investment, and leakages into saving and imports are modest. However, it does not always do so to the same extent — or in real terms — if the economy is near full capacity (causing inflation instead), if it is financed in ways that crowd out private spending, or if much of it leaks abroad. The most defensible conclusion is that higher government spending usually raises national income, but the size (and whether the rise is real or merely nominal) depends on the state of the economy and how the spending is financed.

Saving (S) is a leakage from the circular flow, so a rise in saving withdraws income that would otherwise be spent on domestic output. This is the basis for the claim that more saving harms the economy.

The case that more saving is harmful (short run). If households save more and spend less, leakages rise: firms receive less revenue, cut output and employment, and the circular flow contracts, lowering national income. This is the so-called 'paradox of thrift': if everyone tries to save more at once, lower spending can reduce incomes and even reduce total saving. In a recession, when demand is already weak, a surge in saving can deepen the downturn — clearly harmful in the short run.

The case that more saving is beneficial. Saving is not simply lost from the economy. Saving placed in banks provides funds that can be lent to firms for investment (I) — an injection. Higher investment raises the economy's capital stock and productive capacity, supporting long-run growth and higher future incomes. Saving also helps households build wealth and provides a buffer against future shocks. So in the long run, and provided the savings are channelled into investment, higher saving can be beneficial.

Judgement. A rise in household saving is not always harmful. In the short run, especially in a recession, a sudden rise in saving reduces spending and can lower national income and employment — harmful. But in the long run, saving funds investment that raises productive capacity and growth, which is beneficial. The key determinant is whether the extra saving is borrowed and invested: if banks lend it out for productive investment, the leakage is offset by an injection and growth improves; if it sits idle or confidence is low so firms do not invest, the contractionary effect dominates. The most defensible conclusion is therefore that more saving is harmful chiefly in the short run when demand is weak, but is beneficial in the long run when it finances investment — so the statement that it is always harmful is too strong.