Real vs. Nominal GDP: What's the Difference?

The Core Distinction

Nominal GDP values every good and service at the prices actually prevailing in the period being measured. If output is unchanged but every price rises 5 percent, nominal GDP rises 5 percent. Real GDP values output using prices held fixed relative to a reference period, so that the number changes only when the quantity of goods and services changes. This is why real GDP is the measure used to judge whether an economy grew or contracted: it answers the question of whether more was actually produced, not whether the same production carried a bigger price tag. Nominal GDP is sometimes called current-dollar GDP and real GDP chained-dollar or constant-dollar GDP.

The GDP Deflator and the Arithmetic

The two measures are linked by the GDP deflator, defined as nominal GDP divided by real GDP, multiplied by 100. Rearranged, real GDP equals nominal GDP divided by the deflator, times 100. In the reference year the deflator equals 100 and the two GDP figures are identical by construction. The percentage change in the deflator is one of the standard measures of economy-wide inflation. A useful approximation for exam work: the growth rate of nominal GDP is roughly equal to the growth rate of real GDP plus the inflation rate as measured by the deflator, so if nominal GDP grows 6 percent while prices rise 4 percent, real growth is about 2 percent.

Why the BEA Uses Chain Weighting

Holding prices fixed at a single distant base year produces a well-known distortion: goods whose relative prices are falling, such as computing equipment, tend to be the goods whose quantities are growing fastest, so old price weights progressively overstate their contribution and inflate measured growth. To fix this, the BEA adopted chain weighting in the mid-1990s. Chained real GDP calculates growth between each adjacent pair of periods using prices from both, then links those growth rates together into a continuous series. The result is expressed in chained dollars tied to a reference year the BEA updates periodically. One consequence students should know: chained real GDP components do not add up exactly to the total, which is why published tables carry a residual line.

Which One to Use, and the GDP vs. GNP Trap

Use real GDP for anything involving growth, recessions, comparisons across years, or living standards; use nominal GDP for ratios in which both numerator and denominator are current-dollar amounts, such as debt-to-GDP or the deficit as a share of GDP, and for comparing the size of an economy to a current-dollar quantity. A separate distinction is worth keeping straight: GDP counts production located inside a country's borders regardless of who owns the factors, while GNP counts production by a country's residents and their assets wherever they are located. The United States featured GNP as its headline measure until 1991, when the BEA switched to GDP to match international practice. Per capita real GDP, which divides real GDP by population, is the standard rough proxy for average material living standards — with all the caveats about distribution and non-market activity that Kuznets himself raised.