Gross domestic product (GDP) is the market value of final goods and services produced within a country’s borders over a period. It is the headline scoreboard for economic size and growth: useful, incomplete, and easy to misread.
Three ways to add it up
In principle, GDP can be measured by production (value added by industry), by expenditure (consumption + investment + government spending + net exports), or by income (wages, profits, and other factor incomes). Statistical offices reconcile these approaches. Revisions are normal: early estimates arrive before full data.
In the US, the Bureau of Economic Analysis (BEA) publishes GDP. In the UK, the ONS does. International comparisons often use World Bank or IMF series, sometimes in purchasing-power-parity terms so that living-cost differences are less distorting.
Real vs nominal GDP
Nominal GDP rises with prices and with quantities. Real GDP holds prices constant (using a base year or chain-weighting) so that growth reflects volumes. When headlines say “the economy grew 2%,” they almost always mean real GDP. Nominal growth near inflation with flat real GDP means the economy is not expanding in volume terms.
The GDP deflator connects those two measures. It equals nominal GDP divided by real GDP, times 100. The GDP deflator calculator solves for the deflator, for real GDP, or for nominal GDP.
A quantity theory sketch writes nominal GDP as the price level times real output, then relates that product to money times velocity. The velocity of money calculator runs that arithmetic with numbers you type.
What GDP leaves out
GDP does not measure happiness, inequality, environmental damage, or unpaid household work. A disaster that triggers rebuilding can raise GDP while welfare falls. Leisure, health, and longevity matter for living standards but sit outside the production boundary. GDP per person is a better rough living-standard proxy than total GDP, yet it still averages away distribution.
Business cycles and potential output
Economies expand and contract. Recessions are commonly described as significant declines in activity lasting more than a few months (the US NBER dates recessions judgmentally; many analysts use rules of thumb around GDP and employment). Potential output is a latent estimate of what the economy can sustainably produce without overheating. The gap between actual and potential GDP informs how much spare capacity exists, a concept linked to inflation pressure and unemployment.
One classroom bridge from a growth gap to unemployment is Okun's law. The Okun's law calculator runs that arithmetic in your browser. Read Okun's law for the ideas behind it.
The level comparison behind that story is the output gap. The output gap calculator turns actual and potential output into a percent of potential. Read the output gap for the ideas behind it.
The classroom graph that puts that gap on the page is the aggregate demand and aggregate supply model. A recessionary gap sits to the left of long run aggregate supply. An inflationary gap sits to the right.
UK and US nuances
The US economy is larger and more closed as a share of trade than the UK’s; sterling and financial services give UK GDP a different cyclical flavour. Both countries publish quarterly growth rates that are often annualised in US commentary and presented as quarter-on-quarter or year-on-year in UK commentary. Always check the convention before comparing.
Illustrative only: if real GDP grows about 2% a year while population grows about 0.5%, GDP per person grows near 1.5%. Use BEA, ONS, or World Bank releases for actual figures. Do not treat this site as a live data feed.
Continue with policy tools that try to stabilise growth, or trade for the net-exports piece of the expenditure identity. Glossary: GDP, recession, productivity.
Government spending can move GDP by more than the initial outlay in a simple classroom sketch. The fiscal multiplier calculator turns an MPC into that spending multiplier. The explainer is fiscal multipliers.
Sources
Go deeper: production possibilities curve, output gap, output gap calculator, Okun's law, Okun's law calculator, recession definitions, fiscal multipliers, fiscal multiplier calculator, velocity of money calculator, GDP deflator calculator.