What GDP Measures
Gross domestic product is the market value of all final goods and services produced within a country in a given period. Three words carry the weight:
- Final — only finished output counts. The steel in a car is not counted separately, or it would be double-counted.
- Within — production inside the country's borders, regardless of who owns the firm. GNP counts by ownership instead.
- Market value — only transactions with a price. Unpaid housework, volunteering and the black market are excluded.
The Expenditure Approach
GDP = C + I + G + (X − M)
| Component | What it covers | Typical US share |
|---|---|---|
| C — Consumption | Household spending on goods and services | ~68% |
| I — Investment | Business equipment, construction, inventory changes | ~18% |
| G — Government | Government consumption and investment | ~17% |
| X − M — Net exports | Exports minus imports | −3% |
Imports are subtracted not because they harm the economy but because they were already counted inside C, I or G. Subtracting them removes foreign production from a domestic measure.
Three Ways to Measure the Same Thing
| Approach | Method |
|---|---|
| Expenditure | Add up everything spent on final output |
| Income | Add up all wages, profits, rent and interest earned |
| Production | Add up the value added at every stage |
In principle all three give the same number, because every dollar spent is a dollar earned. In practice they differ slightly, and the gap is published as a "statistical discrepancy".
Nominal and Real GDP
Nominal GDP is measured in current prices, so it rises when prices rise even if nothing more is produced. Real GDP strips inflation out by valuing output in a base year's prices.
Real GDP = Nominal GDP ÷ GDP deflator × 100
GDP deflator = Nominal GDP ÷ Real GDP × 100
A deflator of 118 means prices are 18% above the base year. Growth reported in the news is always real growth; nominal growth of 6% during 4% inflation is only 2% of genuine expansion.
GDP per Capita
Dividing GDP by population gives an average output per person, which is a far better proxy for living standards than total GDP. India's economy is larger than Switzerland's; Swiss GDP per capita is roughly twenty times higher.
For international comparison, economists usually adjust further using purchasing power parity, which accounts for the fact that the same money buys different amounts in different countries. PPP figures narrow the gap between rich and poor countries considerably.
Growth Rates
Annual growth = (GDPend ÷ GDPstart)1/years − 1
This is a compound annual rate, not a simple average. The difference matters over long periods, and the rule of 70 gives a quick sense of scale: divide 70 by the growth rate to get the doubling time. At 2% an economy doubles in 35 years; at 7%, in a decade.
| Annual growth | Doubling time |
|---|---|
| 1% | 70 years |
| 2% | 35 years |
| 3% | 23 years |
| 5% | 14 years |
| 7% | 10 years |
| 10% | 7 years |
What GDP Leaves Out
Simon Kuznets, who built the first national accounts for the United States in the 1930s, warned Congress directly that "the welfare of a nation can scarcely be inferred from a measurement of national income". The criticisms have not changed much since:
- Unpaid work is invisible. Childcare and housework are excluded; paying someone else to do the same work increases GDP.
- Distribution is ignored. Average output says nothing about who receives it.
- Damage counts as output. Cleaning up an oil spill adds to GDP; the spill itself subtracts nothing.
- Depletion is not deducted. Selling off natural resources appears as income rather than as the liquidation of an asset.
- Quality improvements are hard to capture. A phone today is vastly more capable than one from 2005 at a similar price.
- Leisure has no value. A country that produces the same output in fewer hours registers no gain.
Alternatives exist — the Human Development Index, Genuine Progress Indicator, various wellbeing measures — but none has displaced GDP, largely because it is comparable across countries and decades and is collected consistently.
Recession
The common shorthand is two consecutive quarters of falling real GDP. In the United States the official determination is made by the NBER's Business Cycle Dating Committee, which weighs employment, income and industrial production alongside GDP and is not bound by the two-quarter rule.
Frequently Asked Questions
What is the difference between GDP and GNP?
GDP counts production inside the country's borders; GNP counts production by the country's residents wherever it occurs. For most large economies they are close; for countries with large foreign-owned sectors or many workers abroad they diverge sharply.
Why are imports subtracted?
Because they were already included in consumption, investment or government spending. Subtracting them leaves only domestic production, which is what GDP measures.
Does government spending really add to GDP?
Government consumption and investment are counted as final output. Transfer payments such as pensions and benefits are not, because they are not payments for production — they appear later when the recipient spends them.
Is a bigger GDP always better?
Not necessarily. GDP measures activity, not welfare, and rises with pollution clean-up, disaster reconstruction and resource depletion. It is a useful indicator, not a goal in itself.