What is the business cycle?
The business cycle is the recurring pattern of expansion and contraction in a nation’s economic activity over time, typically measured by real GDP. It moves through four phases: expansion, peak, contraction, and trough. Each full cycle runs from one trough to the next, fluctuating around a long-term growth trend.
In simple terms, the business cycle means the economy does not grow in a straight line. It speeds up, slows down, shrinks, and recovers in repeating waves. When people ask what business cycle theory is, they are really asking how and why economies swing between periods of growth and decline.
How a business cycle works
A business cycle works as a continuous loop that repeats over months and years. The economy expands until it reaches a high point, contracts until it hits a low point, then begins expanding again. The peak and trough are the turning points that separate growth from decline.
In the United States, the National Bureau of Economic Research (NBER) is the widely accepted authority that officially dates these peaks and troughs. In its framework, the economy is always in either an expansion or a recession. Cycles are recurring but not fixed in length: using NBER postwar U.S. data, expansions have averaged roughly 64 months while contractions averaged about 10 months, though the duration of any single cycle varies enormously.
The 4 phases of the business cycle
| Phase |
What happens |
Key signs |
| Expansion |
Economic activity rises |
GDP grows, unemployment falls, spending and investment climb, and credit is cheap |
| Peak |
Growth tops out |
GDP and employment hit their highest levels, and inflation pressure is building |
| Contraction |
Economic activity declines |
GDP falls, unemployment rises, spending and profits shrink (a deep, broad contraction is a recession) |
| Trough |
Activity bottoms out |
GDP and employment hit their lowest levels before the recovery began |
What causes the business cycle?
There is no single cause. Business cycles are usually driven by a mix of forces, commonly grouped into three categories:
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Demand-side factors: shifts in consumer and business spending, confidence, interest rates, and credit availability. Keynesian theory ties cycles largely to swings in aggregate demand.
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Supply-side factors: changes in productivity, technology, labour, and input or commodity costs.
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External shocks: unexpected events such as pandemics, wars, financial crises, or sharp oil-price moves.
Business cycle indicators
Economists and traders track the economy’s phase using three types of indicators:
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Leading indicators change before the economy does and help anticipate turning points, for example, stock market trends, consumer confidence, and new business orders.
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Coincident indicators move in step with the economy in real time, such as GDP, industrial production, and retail sales.
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Lagging indicators confirm a trend after it has occurred, such as the unemployment rate, corporate earnings, and inflation.
Watching these together helps identify which phase the business cycle is currently in, though no indicator predicts turning points with certainty.
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