Gross Domestic Product (GDP)

Gross domestic product is the total market value of the final goods and services produced within a country's borders over a stated period. The word "final" is doing work: GDP counts finished goods and services sold to their end user, not the intermediate parts and materials bought along the way, so a loaf of bread is counted but not separately the flour the baker bought, which would double-count. In the United States the figure is estimated and published by the Bureau of Economic Analysis (BEA), and its rate of change from one period to the next is the standard way to say whether the economy grew or shrank.

GDP is most often built up through the expenditure approach, which adds four categories of spending: consumption by households, investment by businesses (including construction and inventories), government spending on goods and services, and net exports, meaning exports minus imports. That last term is why a surge in imports, by itself, subtracts from the GDP calculation. Adding these gives the total value of what the economy produced, because everything produced is ultimately bought by someone.

The single most important distinction is between nominal and real GDP. Nominal GDP is measured in current dollars, at the prices that prevailed during the period. That is a problem for comparisons across time, because output can look like it grew simply because prices rose. Real GDP removes the effect of inflation, restating output in constant dollars so that a change in real GDP reflects a change in the quantity of goods and services produced rather than in their prices. When economists talk about "GDP growth" or whether the economy is expanding, they almost always mean real GDP. The adjustment relies on the same price-measurement problem that inflation itself describes.

GDP is a flow measured over time, and the BEA releases it in stages. An advance estimate for a quarter arrives about a month after the quarter ends, followed by a second and a third estimate as more complete data come in, each of which can revise the earlier figures. That means an early GDP number is a preliminary reading that may move, sometimes materially, which matters when a single quarter's figure is treated as decisive.

That staged, revisable quality is one reason the familiar shorthand, that two consecutive quarters of falling real GDP means a recession, is only a rule of thumb. In the United States, recessions are dated by the National Bureau of Economic Research using a broader set of indicators, and its dates do not always line up with the two-quarter rule. GDP is a central input to that judgment but not the whole of it, so a recession call and the two-quarter test can diverge. GDP also says nothing about how output is distributed or about wellbeing; it measures the size of the pie, not how it is shared.

GDP is compiled by adding up the economy's spending on final output and then, for real GDP, adjusting that total for price changes so different periods can be compared. Growth is reported as the percentage change from the prior period, usually stated as an annualized rate.

A hypothetical shows the nominal-versus-real trap. Suppose an economy produces exactly the same physical output in Year 2 as in Year 1, no more cars, houses, or haircuts, but prices across the board rose 4%. Nominal GDP, measured in current dollars, would be 4% higher in Year 2 and might be reported as "4% growth." Real GDP, which holds prices constant, would show 0% growth, correctly reflecting that the economy produced no more than before. The entire apparent gain was inflation. This is why the real figure, not the nominal one, is used to judge whether an economy is genuinely expanding.

What GDP is good for

• A single, comparable gauge of the size of an economy and whether it is growing or contracting.
• Widely available and consistently measured, which makes it useful for comparisons across time and across countries.
• Real GDP growth is a core input to judging the business cycle and to policy decisions.

What GDP does not capture

• It measures the size of output, not how income is distributed or whether people are better off.
• Early estimates are preliminary and can be revised substantially.
• It excludes unpaid work, much of the informal economy, and environmental costs, so it is an incomplete picture of welfare.