Lesson preview · How money moves through an economy
The circular flow, leakages and injections
~7 min · Free to read
Imagine you buy a 10-dollar lunch at a café. For you, that is spending. For the café, it is income. The café pays its cook, who spends part of her wage on a bus ticket. Now the bus company has income too. Your 10 dollars wasn’t used up. It moved on.
Economists call this loop the circular flow of income: a map of how money moves round an economy.
Key Term
Households, firms and two markets
The simplest model has two groups, called sectors.
- Households are people. They own the factors of production, the inputs firms need: labour, land, capital (machines and buildings) and enterprise (business skill and risk-taking).
- Firms are businesses. They hire those factors to make goods and services.
They meet in two markets. In the factor market, households sell labour and other factors to firms. Firms pay them income: wages, rent, interest and profit. In the goods market, households spend that income on what firms make.
In each market, money goes one way and real things go the other. Every dollar a household spends becomes a firm’s income, and the firm pays it back to households as wages, rent, interest and profit. In this simple model, households spend all of their income, so total spending equals total income.
Key Term
Leakages and injections
In a real economy, not all income comes back to firms as spending.
- A leakage is income that leaves the loop instead of being spent on goods and services made in the country.
- An injection is spending that joins the loop from outside it.
They come in three pairs:
- Taxes (T) leak out; government spending (G) flows in.
- Saving (S) leaks out; investment (I), firms buying new machines and buildings, flows in.
- Imports (M) leak out; exports (X) flow in.
Nothing forces the two halves of a pair to match. Firms can invest more or less than households save. Exports can be bigger or smaller than imports. A government can spend more or less than it collects in tax. So total leakages and total injections can differ.
Adding the government and other countries opens the loop: taxes and imports carry money out (leakages), while government spending and exports bring money in (injections).
Key Term
When injections are bigger than leakages
If injections are bigger than leakages, more money joins the loop than leaves it. Firms sell more, so they make more and hire more, as long as there are spare workers and machines to use. National income (the total income everyone in the country earns) rises. If leakages are bigger, it falls. Income stops changing only when the totals are equal.
Worked Example
In one year in Country X (all figures in billions of dollars), households save 120, pay 200 in taxes and spend 80 on imports. Firms invest 150, the government spends 230, and buyers abroad spend 70 on the country’s exports. Will national income rise or fall?
Key Term
The multiplier effect
Say the government spends an extra 100 million dollars on a bridge. That becomes the builders’ income. They spend part of it in shops, so shopkeepers earn more and spend part again. Each round is smaller, because some income leaks out as tax, saving or imports.
This is the multiplier effect: in this model, an injection raises national income by more than the injection itself. The reason is that one person’s spending is another person’s income.
Real economies are messier. Many studies find that extra government spending raises national income by about the same amount, or by less.
Trap · Common Misconception
"Once money is spent, it's gone"
Your 10 dollars has left your pocket, but the café has it now. Spending moves money from one person to another. That’s why one injection can raise incomes again and again.
Trap · Common Misconception
"Saving always comes straight back as investment"
Saved money leaks out. It comes back only if someone borrows it and spends it, for example a firm buying new machines or buildings. Firms invest for their own reasons, such as the sales they expect. If households save more but firms don’t invest more, spending falls, and so does national income.
Tip
Taxes or government spending: which is which?
Judge each flow from the loop’s point of view, not the government’s. Tax is money in for the government, but households can no longer spend it with firms: a leakage. Government spending leaves the government but reaches firms: an injection.
Tip
How big is the tax leakage?
A country’s GDP (gross domestic product) is the value of all the final goods and services it produces in a year. The OECD (Organisation for Economic Co-operation and Development) is a group of 38 mostly high-income countries. In 2024 (early figures), their taxes averaged about 34% of GDP, from about 18% in Mexico to about 45% in Denmark. That is a big leakage, but governments spend the money again, so much of it flows back in.
Practice · 1 / 6
Ana works in a bakery, which pays her 400 dollars a week. Where does this payment appear in the circular flow?
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