The business cycle is the pattern of expansions and contractions in aggregate economic activity, visible in production, employment, income, and spending. A central subject of macroeconomics, it concerns movements across an economy rather than the fortunes of an individual firm. “Cycle” does not imply a fixed timetable: fluctuations recur, but their duration, severity, and underlying causes vary. Business cycles are also distinct from long-term economic growth, although prolonged downturns can affect an economy’s productive capacity. (elibrary.imf.org)
Phases and turning points
A cycle is conventionally described through expansion, peak, contraction, and trough. During an expansion, overall activity increases; a peak marks the transition to decline. A contraction ends at a trough, after which activity begins rising again. The early expansion is often called a recovery. Recovery does not necessarily mean that output or employment has already regained its previous peak: an economy can be expanding while remaining below earlier levels. (nber.org)
A recession is a substantial, broadly distributed decline in economic activity. Two consecutive quarters of falling real gross domestic product constitute a common shorthand, but not a universal definition. In the United States, the National Bureau of Economic Research weighs the depth, breadth, and duration of decline rather than applying that rule mechanically. A depression denotes exceptionally severe economic weakness, without a universally accepted numerical threshold; the Great Depression is the best-known historical example. (nber.org)
Measurement and identification
Real GDP measures output after accounting for price changes, making it more informative about production than nominal GDP alone. Nevertheless, cycle dating generally uses several indicators because no single series captures the whole economy. Employment, real income, industrial production, and sales can provide complementary evidence, and their turning points need not coincide exactly. Researchers distinguish economy-wide movements from isolated sectoral declines. (imf.org)
A classical business cycle tracks changes in the level of activity. A growth cycle instead tracks deviations from an estimated long-term trend: an economy may experience a growth-cycle downturn while output continues increasing, but more slowly than its trend. The output gap compares actual output with potential output, a related but model-dependent concept. Neither statistical trend nor potential output is directly observed, so conclusions depend partly on estimation methods. (oecd.org)
Analysis of economic time series commonly uses seasonal adjustment to separate recurring calendar effects from cyclical movements. Leading indicators attempt to anticipate turning points, whereas coincident indicators describe contemporaneous activity. OECD composite leading indicators are designed primarily to signal growth-cycle turning points, not to predict precise GDP growth rates. Data revisions and estimation uncertainty limit real-time interpretation. (oecd.org)
Causes and transmission
Business-cycle explanations distinguish initiating shocks from mechanisms that spread or prolong their effects. Shocks may arise from changes in spending, technology, input costs, or financial conditions. An initial disturbance can pass between sectors and countries through income, production, credit, and trade. Different recessions therefore need not share a single cause or propagation mechanism. (imf.org)
Changes in aggregate demand affect firms’ sales and production decisions. Weaker household spending or business investment can reduce employment and income, which further depress spending. Investment and industrial production often decline proportionately more than consumption during recessions. Conversely, adverse supply disturbances, such as higher oil prices, can reduce production while increasing inflation, creating a different pattern from a demand-driven downturn. (imf.org)
Financial conditions can amplify these movements. Expanding credit and rising property values may reinforce one another; reversals can restrict borrowing and spending. Banks, borrowers’ balance sheets, and the value of collateral thus connect financial developments with real activity. BIS research distinguishes a financial cycle, commonly measured through credit and property prices, that can last considerably longer than a conventional business cycle. Their peaks and troughs need not coincide. (bis.org)
Main theoretical approaches
Keynesian economics, associated with John Maynard Keynes, emphasizes fluctuations in spending and the possibility that insufficient demand sustains unemployment. Modern New Keynesian models incorporate slow adjustment of prices and wages, allowing demand and monetary disturbances to affect real output in the short run. Expectations and financial frictions also feature in extensions of these models. (imf.org)
Real business cycle theory instead emphasizes real disturbances, particularly changes in production technology, and models households and firms adjusting their decisions to those disturbances. Fluctuations in productivity are central to its standard formulation. These approaches differ in their assumptions and interpretation of fluctuations; contemporary research also examines interactions among real, monetary, and financial forces rather than treating them as mutually exclusive explanations. (elibrary.imf.org)
Stabilization policy
Monetary policy influences spending and financing conditions through interest rates and other instruments. Fiscal policy affects activity through public spending, taxation, and transfers. Their effects depend on economic conditions, policy design, and transmission delays; measures that support demand do not necessarily resolve constraints on production. Inflation and financing pressures can limit the scope for stabilization. (imf.org)
Automatic stabilizers operate through existing budget rules rather than new discretionary decisions. During downturns, falling tax receipts and increased eligibility for certain transfers can cushion disposable income and spending. Discretionary measures require separate decisions and may face implementation delays. Assessing either approach requires distinguishing cyclical changes in the budget from policy changes and considering the government’s capacity to finance additional expenditure. (imf.org)