Gross Domestic Product

National accountants build GDP three ways and, in principle, arrive at the same total. The expenditure approach sums final spending: household consumption, gross private investment (including the change in business inventories), government consumption and investment, and exports less imports. Imports are subtracted because they are foreign, not domestic, production already embedded in the other categories.

The income approach sums what production pays out: employee compensation, gross operating surplus and mixed income of the self-employed, plus taxes less subsidies on production, with consumption of fixed capital added to move from net to gross. The value-added approach sums each producer's sales less its purchased inputs across every industry, which is exactly why the intermediate transactions between firms cannot inflate the total. In published accounts a statistical discrepancy reconciles the expenditure and income measures.

Nominal GDP values output at current prices, so it rises when quantities rise, when prices rise, or both. Real GDP holds prices fixed to isolate the volume of production. The bridge is the GDP deflator: divide nominal GDP by real GDP and multiply by one hundred. Rearranged, real GDP equals nominal GDP divided by the deflator, times one hundred, and the percentage change in the deflator is a broad measure of domestic price inflation.

The deflator differs from the consumer price index in coverage and construction. It spans everything produced domestically, including investment goods and government output, and its implicit weights shift each period with the composition of output, whereas a consumer price index tracks a fixed household basket. Modern accounts use chain-weighting rather than a single distant base year, which limits the distortion that arises when relative prices and quantities drift far from the reference period.

In the United States the Bureau of Economic Analysis publishes quarterly GDP at a seasonally adjusted annual rate, so a reported figure is the growth pace that would result if the quarter's rate persisted for a year. Estimates arrive in successive vintages as source data improve, and revisions can be large enough to change the narrative. Cross-country work uses GDP per capita, converted at purchasing power parity rather than market exchange rates, to compare living standards.

GDP is territorial. Gross national product, and its modern counterpart gross national income, instead measure output attributable to a country's residents by adding net factor income received from abroad. The distinction matters for economies with heavy foreign ownership of domestic production or large remittance and profit flows. Analysts also compare actual GDP with estimated potential GDP; the gap between them signals slack or overheating and feeds directly into inflation forecasts and policy expectations.

Be able to complete the expenditure identity when one component is missing, and to treat the change in inventories as investment rather than as a residual. Know what is excluded: transfer payments and other government spending that buys no current output, purely financial transactions, unpaid household production, and unrecorded or illegal activity. Government purchases of goods and services count; pensions and unemployment benefits do not.

On the quantitative side, expect to convert between nominal and real GDP using a deflator, to compute the deflator from the two GDP series, and to derive real growth from nominal growth and inflation. Qualitatively, be ready to explain why the income and expenditure approaches must agree, why GDP overstates welfare, and how a GDP figure differs from gross national income for a given economy.