The components of the circular flow of income

The economy consists of two main groups: firms and households. Firms manufacture goods and services, which form the national output. Households supply the factors of production, including labour, land, and capital, that firms need to create this output.

In return, firms pay households for these factors, generating the national income. Households then use this income to buy the goods and services produced by firms, creating the national expenditure.

This relationship can be summarised by the equation:

$\text{National output}=\text{national income}=\text{national expenditure}$

Types of flows in the economy

The circular flow involves two distinct types of movement:

• Physical flow - This includes the real resources exchanged, such as goods and services produced by firms, and the factors of production (labour, land, and capital) provided by households.
• Monetary flow - This refers to the money circulating in the opposite direction, including payments from firms to households for factors of production, and spending by households on goods and services.

Injections and withdrawals in the economy

The circular flow assumes that if households spend all their earnings and firms reinvest all revenues in production, the national output and income remain stable. However, external factors disrupt this balance through injections and withdrawals.

Injections into the circular flow

Injections add extra money directly to firms, boosting the flow:

• Exports - Sales of goods and services to foreign buyers bring in additional revenue.
• Investment - Spending by firms on new equipment or by others on assets like buildings.
• Government spending - Public expenditure on infrastructure, services, or subsidies.

Withdrawals from the circular flow

Withdrawals remove money from the cycle, reducing the flow. These can occur from households or firms:

• Imports - Purchases of foreign goods and services send money abroad.
• Savings - Money set aside by households or firms instead of being spent.
• Taxes - Payments to the government that reduce available funds for spending.

Economic equilibrium and changes

Economic equilibrium occurs when the total injections equal the total withdrawals, keeping the circular flow stable and the national output unchanged.

Effects of imbalances between injections and withdrawals

• Injections greater than withdrawals - This leads to higher expenditure than output, prompting firms to increase production. As a result, national output, income, and expenditure all rise.
• Withdrawals greater than injections - This causes output to exceed expenditure, leading firms to cut back production. Consequently, national output, income, and expenditure all fall.

The multiplier effect

An injection into the circular flow often results in a larger overall increase in national income than the initial amount injected, due to the multiplier effect. This happens as the injected money circulates multiple times, with portions spent and respent before leaking out.

For example, government spending on a project pays households for resources, who then spend part of it on goods, generating more income for firms, and so on. However, at each stage, some money leaks out through withdrawals like taxes, savings, or imports.

The size of the multiplier depends on the rate of these leakages: higher withdrawals mean money exits faster, resulting in a smaller multiplier. Conversely, lower leakages allow the effect to build more significantly.

If a large share of spending goes to imports, savings, or taxes, the multiplier remains small because the injection quickly leaves the domestic cycle.

Worked example - Calculating the impact of the multiplier effect

The government injects £75 million into a new road project. Assume that at each stage, 25% of the additional income leaks out as withdrawals (savings, taxes, and imports), while 75% is respent. Calculate the total increase in national income after the multiplier effect.

Step 1: Identify the values

• Initial injection = £75 million
• Proportion respent (MPC equivalent) = 0.75
• Proportion withdrawn (MPW equivalent) = 0.25

Step 2: Apply the multiplier formula

$\text{Multiplier}=\frac{1}{\text{MPW}}$ $\text{Multiplier}=\frac{1}{0.25}=4$

Step 3: Calculate the total increase

Total increase = initial injection × multiplier Total increase = £75 million × 4 = £300 million

The difference between wealth and income

Income represents the ongoing flow of money earned by households and firms, such as wages or revenues, which circulates in the economy.

In contrast, wealth is the accumulated stock of assets owned by individuals or firms, including cash savings, property like houses, or items like vehicles. Wealth acts as a reserve that is not actively part of the current circular flow but could enter it later.

Although distinct, income and wealth often correlate: higher income enables greater savings and asset purchases, leading to increased wealth over time.