Macroeconomics · Unit 2: Economic Indicators and the Business Cycle · 40 min read · Updated 2026-05-13
The Circular Flow and GDP — AP Macroeconomics
AP Macroeconomics · Unit 2: Economic Indicators and the Business Cycle · 40 min read
1. The Basic Circular Flow Model★☆☆☆☆⏱ 10 min
The circular flow diagram is a simplified model of a closed private economy that illustrates how money, resources, and goods move between two core groups: households and firms.
Households own all factors of production (labor, land, capital, entrepreneurship) and sell them to firms to earn income
Firms use factors of production to create goods and services, which they sell to households to earn revenue
There are two core markets: the resource (factor) market for factors of production, and the product market for finished goods and services
2. GDP: Definition and Counting Rules★★☆☆☆⏱ 15 min
Each part of the GDP definition has a specific rule for what to count and what to exclude, which is heavily tested on the AP exam:
Only final goods are counted; intermediate goods (used to produce other goods) are excluded to avoid double counting
Only newly produced goods are counted; used goods produced in previous years are excluded
Only production inside the country's borders is counted, regardless of the producer's nationality
Non-market production (e.g. home cooking for your family) and illegal activity are excluded
3. Calculating GDP: The Expenditure Approach★★☆☆☆⏱ 15 min
Because every dollar spent on a good is a dollar of income for the producer, GDP can be calculated two equivalent ways: the expenditure approach (summing all spending) and the income approach (summing all income). The expenditure approach is the most commonly tested on the AP exam.
Key notes on components: Net exports equal exports minus imports; transfers payments (like Social Security or unemployment benefits) are not counted in government purchases, because they do not pay for new production.
Common Pitfalls
Why: GDP only counts newly produced goods; the car was produced in the year it was originally manufactured
Why: The value of intermediate goods is already included in the final good's price, so counting it twice inflates GDP
Why: Transfer payments are just reallocations of existing money, not payments for new production
Why: GDP counts production within a country's borders, regardless of producer nationality