The Circular Flow of Income and Expenditure

The circular flow of income is a model showing how money, goods, services, and factors of production move continuously between the different sectors of an economy in a never-ending circle. Its central insight is that in an economy, one person's spending is always another person's income — so income, output and expenditure are simply three different ways of viewing the same continuous circular process. This is why national income can be measured by the income method, the output (product) method, or the expenditure method, and all three, in principle, give the same total.

The two-sector economy (households and firms). The simplest model has just two sectors: households, who own all the factors of production (land, labour, capital, enterprise), and firms, who produce all the goods and services. There are two flows running in opposite directions. First, the REAL flow: households supply factor services (labour, land, capital) to firms, and firms supply finished goods and services back to households. Second, the MONEY flow, running the opposite way: firms pay households factor incomes (rent, wages, interest, profit) for their factor services, and households spend that income buying goods and services from firms (consumption expenditure). In this simplest model — assuming households spend ALL their income and there is no government or foreign trade — the total income paid out by firms equals the total expenditure households make, which equals the total value of output produced. Income = Output = Expenditure, flowing round in a closed, self-sustaining circle.

The circular flow at a glance — two loops, opposite directions:

The two loops circulate simultaneously in opposite directions: households send factor services to firms and get goods back (the real flow), while firms send factor incomes to households and get consumption spending back (the money flow).

Leakages and injections. The simple circle keeps flowing steadily only if all income earned is passed straight back as spending. In reality, some income LEAKS out of the circular flow, and some spending is INJECTED into it from outside. A LEAKAGE (or withdrawal) is any income NOT passed on directly as spending on domestic output — it reduces the circular flow. An INJECTION is any spending added to the flow that does NOT come from households' current spending of their income — it increases the flow. When total leakages equal total injections, the circular flow is in equilibrium and national income is stable; when they are unequal, income rises or falls until balance is restored.

The three-sector economy (adding the government). When we add the government, two new flows appear. The government withdraws TAXES from households and firms (a leakage), and it puts back GOVERNMENT EXPENDITURE — spending on public goods, salaries of government employees, and transfer payments (an injection). If the government spends exactly what it collects in taxes, the flow is undisturbed; a budget deficit (spending more than it taxes) injects more than it withdraws, expanding the flow, while a surplus does the opposite. …