What Drives GDP Growth — and What Follows From It

What GDP Is Built From

Consumption (C): Household spending on goods and services. It is the largest single component of U.S. GDP by a wide margin, so consumer behavior dominates quarter-to-quarter movement.
Investment (I): Business spending on structures, equipment, and intellectual property, plus residential construction and the change in private inventories. It is a small share of the total but by far the most volatile, which is why it drives so much of the cycle.
Government purchases (G): Federal, state, and local spending on goods and services. Transfer payments such as Social Security are excluded, because they are not payments for current production.
Net exports (X - M): Exports minus imports. Imports are subtracted because they were counted once already inside C, I, or G but were not produced domestically.

What Makes Real GDP Rise or Fall

Labor input: More hours worked, whether from population growth, higher participation, or falling unemployment, mechanically raises output.
Capital and productivity: Over long horizons, growth comes mostly from more capital per worker and from technological progress rather than from more workers.
Credit conditions: Interest rates and lending standards govern how much investment and housing activity firms and households undertake.
Fiscal and monetary policy: Tax and spending changes and central bank rate decisions shift aggregate demand, with lags.
Inventory swings: Firms building or drawing down stockpiles can add or subtract meaningfully from a single quarter without any change in underlying demand.
Shocks: Energy price spikes, financial crises, pandemics, strikes, and natural disasters can move output sharply and suddenly.

What a Contraction Sets in Motion

Rising unemployment: Okun's law describes the empirical tendency for the unemployment rate to rise when output growth falls short of its potential rate.
Falling tax revenue and rising outlays: Income and sales tax receipts drop while unemployment insurance and other automatic stabilizers pay out more, widening deficits without any new legislation.
Policy response: Downturns typically bring interest rate cuts and, often, discretionary fiscal support.
Business retrenchment: Firms delay capital projects and run down inventories, which deepens the initial decline before it reverses.
Debt ratios: Because debt-to-GDP has output in the denominator, a contraction raises the ratio even if the level of debt is unchanged.

How Recessions Are Actually Dated

The widely repeated definition — two consecutive quarters of falling real GDP — is a rule of thumb popularized in the 1970s, not the official standard. In the United States, business cycle turning points are determined by the Business Cycle Dating Committee of the National Bureau of Economic Research, a private nonprofit research organization, not by the BEA, the Federal Reserve, or the White House. The committee defines a recession as a significant decline in economic activity that is spread across the economy and lasts more than a few months, and it weighs depth, diffusion, and duration together. It looks at a range of monthly series — including payroll employment, household employment, real personal income less transfers, real consumer spending, real manufacturing and trade sales, and industrial production — rather than at quarterly GDP alone. Because it waits for revised data, the committee typically announces a turning point many months after the fact.