What Is the Business Cycle? Phases and How It's Measured

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The business cycle is the recurring pattern of expansion and contraction in a country’s aggregate economic activity. During an expansion, output, employment, income and sales rise together across many industries at roughly the same time. A similarly broad decline follows, then another expansion. The sequence repeats, but the length and severity of each phase vary from one cycle to the next, so the business cycle is a pattern rather than a fixed timetable. It is also called the economic cycle or trade cycle.

The Four Phases of the Business Cycle

A business cycle diagram is usually drawn as a wave around an upward-sloping trend line, the economy’s long-run growth path. The wave shows activity moving above and below that path:

1. Expansion. Output grows, firms hire, incomes rise and consumers spend more. Rising sales encourage more production, which supports further hiring, a self-reinforcing loop.
2. Peak. Activity reaches its high point before turning down. A peak is a single turning point, not a period of strong growth.
3. Contraction. Output, employment, income and sales fall. A recession happens within a contraction, though the two terms are not identical (see below).
4. Trough. The low point. Once activity stops falling and begins to rise, a recovery starts and a new expansion begins.

The cycle is measured from one point to the matching point: trough to trough or peak to peak. An expansion runs from a trough to the next peak, and a contraction runs from that peak to the following trough.

What Drives the Cycle

No single cause explains every cycle, and economists emphasize different forces. Commonly cited drivers include swings in consumer and business spending, credit conditions and interest rates set by central banks, supply shocks such as sudden jumps in energy prices, and waves of innovation. Joseph Schumpeter, for example, tied cycles to the arrival and spread of new technologies. What all cycles share is co-movement: many economic variables move in the same direction at the same time, which separates a business cycle from a downturn confined to one sector.

How the Business Cycle Is Measured

Coincident Indicators

Aggregate activity is not captured by one number. The NBER looks at real (inflation-adjusted) gross domestic product as the broadest measure of output, together with industrial production, employment, real income and wholesale-retail sales. These are coincident indicators: they move with the cycle rather than ahead of or behind it. Real figures matter because rising prices can lift nominal GDP even when actual output is flat.

The Three D’s

The severity of a recession is judged on three dimensions:

• Depth: the size of the peak-to-trough decline in output, employment, income and sales.
• Diffusion: how widely the decline spreads across industries, activities and regions.
• Duration: the time between the peak and the trough.

A shallow decline that lasts many months, or a sharp but short drop that hits nearly every industry, can both qualify as a recession. The NBER’s Business Cycle Dating Committee has described a recession as a significant decline in economic activity spread across the economy, lasting more than a few months and normally visible in real GDP, real income, employment, industrial production and wholesale-retail sales.

Worked Example (Hypothetical)

Suppose a fictional economy’s real GDP index reads 100 at a peak in month 0, falls steadily to 96 by month 10, then starts rising and returns to 100 by month 22.

• Depth: (100 − 96) ÷ 100 = 4% peak-to-trough decline in output.
• Duration of the contraction: month 0 to month 10 = 10 months.
• Recovery time to the prior peak: month 10 to month 22 = 12 months.

If employment, income and sales also fell over those months across most industries, the episode shows the depth, diffusion and duration of a recession. If only manufacturing output fell while services and employment kept growing, diffusion would be low, and it might not be classified as a recession at all. Note that the expansion is counted from the trough (month 10), not from the month the index regains 100.

Dating Business Cycles

The NBER sets the official U.S. chronology of peaks and troughs, and it does so with a long lag. Data are revised for months or years, and the committee waits until the turning point is clear. The recession that began in late 2007 ended in June 2009, but the committee announced that trough on September 20, 2010, after waiting for revisions to the National Income and Product Accounts released that July and August. By the time a recession is officially dated, the economy has often been recovering for over a year.

The historical record shows how unequal the phases are. From 1945 to 2019, the average U.S. expansion lasted about 65 months and the average recession about 11 months. Between the 1850s and World War II, the averages were about 26 months for expansions and 21 months for recessions. The longest expansion on record ran from 2009 to 2020, lasting 128 months. At the other extreme, the Great Depression contained several recessions, one of which lasted 44 months.

Business Cycle vs. Related Terms

Contraction vs. recession. A contraction is the phase from peak to trough. A recession is a significant, broad and lasting decline within that phase. Not every contraction becomes a recession, and a recession need not cover the entire contraction.

The two-quarter rule. Two consecutive quarters of falling real GDP is a widely used rule of thumb for a recession, but it is not the NBER’s definition. The committee weighs several monthly indicators, so a recession can be declared without two negative GDP quarters, and two negative quarters do not automatically produce one.

Business cycle vs. market cycle. The stock market is not the economy. Market cycles are measured with broad stock indexes, and their turning points often differ from those of the business cycle.

Cycle vs. trend. Long-run growth comes from expanding labor, capital and productivity. The business cycle describes short-term swings around that trend, so an economy can be growing over decades while passing through several recessions.

Stock Prices and the Business Cycle

The largest stock market declines have tended to occur around contractions and recessions. During the Great Recession, the S&P 500 fell about 57% between October 9, 2007, and March 9, 2009.

The mechanism runs through expectations. When layoffs, rising unemployment or falling output raise fears of a recession, businesses cut hiring and investors shift toward assets expected to preserve capital, so prices of growth-oriented investments drop, often before the contraction shows in official data. Anticipation of weaker profits, not the contraction itself, pushes prices down. For the same reason, markets often start rising before the trough, while economic data still look poor.

How the Business Cycle Is Used

Policymakers use the cycle to time responses: central banks may lower interest rates during contractions and raise them when an expansion pushes inflation higher, and governments may adjust spending and taxes. Businesses use it for hiring, inventory and investment plans. Investors use it to think about which sectors tend to hold up in downturns and which depend on strong demand.

Limitations of the Business Cycle

• Not predictable. Economies are complex and interconnected; shifts in inflation or production can hint at change, but calling a turning point in advance is very difficult.
• Irregular phases. Historical averages do not tell you how long the current expansion or recession will last.
• Identified late and revised. Official dates arrive long after the fact, and early GDP and income readings are revised, which limits their use for real-time decisions.
• National focus. Each country has its own cycle and its own dating method; the NBER chronology applies to the United States.

The Bottom Line

The business cycle matters to policymakers, businesses and investors who plan around expansions and downturns. Official NBER dates arrive long after turning points, and historical averages cannot predict how long the current phase will last. Since stock prices often fall before a contraction shows in data and rise before the trough, the cycle works best as a framework for understanding conditions rather than a timing tool.