One sector's expenditure can become another sector's income.
The circular flow links households, firms, government and the foreign sector. Households supply factors of production and receive incomes; firms sell output and pay factor incomes. Spending on domestic production generates receipts that support incomes. Saving, net taxes and imports withdraw spending from the simple domestic income-consumption flow; investment, government purchases and exports inject spending. These are flows over a period, not accumulated stocks. Saving does not disappear: financial institutions can help channel funds to investment, although saving and planned domestic investment need not be equal at every income level.
- Four sectors
- Households, firms, government and the foreign sector exchange resources, income and spending. For example, a household supplies labour to a firm, receives wages and uses some of them to buy its output.
- Withdrawals
- Saving (S), net taxes (T) and imports (M) leave the immediate domestic consumption flow. Net taxes mean taxes paid minus transfers received from government.
- Injections
- Investment (I), government purchases (G) and exports (X) add spending to the flow. Investment here buys productive equipment or adds inventories, rather than simply changing ownership of existing shares.
Apply the idea
Financial channel
A household can save through a bank, while a firm obtains bank finance to buy equipment. Financial institutions and markets connect saving with investment funding. The decisions remain separate: more saving does not guarantee an equal planned equipment purchase at every income level.
Flow equilibrium
In a consistent simple four-sector model, planned injections I + G + X equal planned withdrawals S + T + M at equilibrium. T here means net taxes, using the same accounting convention throughout.
Time and stocks
A flow is measured over a period: saving $200 during a month. A stock is measured at a date: the total savings balance held at month-end. Do not compare a monthly flow with an accumulated balance as if they were the same measure.
Worked example: Where one household's $1,000 goes
A household receives $1,000 of income this month. It spends $600 on domestically produced consumption, $100 on imported consumption, saves $200 and pays $100 in net taxes. Separately, a firm orders new equipment and overseas visitors buy local services.
- The household allocation totals $1,000. The $100 imported purchase is part of its consumption expenditure but does not directly buy domestic production.
- Saving $200, net taxes $100 and imports $100 are withdrawals of $400 from the domestic consumption flow.
- The equipment order is investment expenditure and the foreign visitors' local purchases are exports of services: both can inject demand for domestic output.
- Taxes can finance government purchases, but the tax receipt and purchase are separate flows. One household's allocation alone does not establish economy-wide equilibrium.
Watch out for this
Imports vanish from the world economy and saving can never support spending.
They are withdrawals from this domestic spending stream. Imports purchase foreign output, while saving can finance investment through financial channels.
Check your understanding
A resident pays for a holiday service produced overseas. Which withdrawal does the purchase represent?
- Investment.
- Government purchases.
- An import of services.