GDP Deflator

The GDP deflator is a price index that measures the change in prices of all the final goods and services produced in an economy. It is calculated by dividing nominal Gross Domestic Product (GDP), measured at current prices, by real GDP, measured at the constant prices of a base year, and multiplying by 100. Because it covers the whole of domestic output rather than a fixed shopping basket, it is the broadest single measure of inflation in an economy.

The deflator is a by-product of the national accounts, compiled under the UN System of National Accounts (SNA) by statistics offices such as the US Bureau of Economic Analysis and the Pakistan Bureau of Statistics (PBS). It is often called the implicit price deflator, because it is not built from a separate price survey but falls out of the gap between nominal and real GDP. It is usually read alongside the Consumer Price Index (CPI), which it often tracks but does not match.

Suppose a bakery sold 1,000 loaves last year and 1,000 loaves this year, but its takings rose by 10%. The bakery did not make more bread; it charged more for it. Comparing this year's takings with what the same loaves would have earned at last year's prices tells you how much of the rise was just higher prices.

The GDP deflator does the same thing for a whole country. It takes everything the economy produced this year, values it once at today's prices and once at base-year prices, and compares the two. The gap is the part of economic growth that came from rising prices rather than from producing more.

The GDP deflator for year $t$ is:

• $\text{Nominal GDP}_t$ is the value of the year's output at that year's prices.
• $\text{Real GDP}_t$ is the value of the same output at base-year prices.
• The deflator equals 100 in the base year, by construction.

Worked example: a country's nominal GDP is 1,320 billion and its real GDP at base-year prices is 1,100 billion. The deflator is $1{,}320 \div 1{,}100 \times 100 = 120$, so prices across the economy are 20% higher than in the base year. If last year's deflator was 112, the GDP deflator inflation rate this year is $(120 - 112) \div 112 \approx 7.1\%$.

The same formula can be turned round to get real GDP from nominal GDP and a known deflator, which is what "deflating" a series means:

Real GDP itself is built from the three national accounting approaches, output-based GDP, expenditure-based GDP and income-based GDP. On the output side, statisticians deflate the Gross Value Added (GVA) of each industry using price indices such as the Wholesale Price Index (WPI) and the CPI, then add the results; the overall deflator is what remains when nominal GDP is divided by that total.

The two measures answer different questions:

• Coverage. The deflator covers everything produced at home, including investment goods such as Gross Fixed Capital Formation (GFCF) and government services. The CPI covers only what households buy.
• Imports. Imported goods are in the CPI but not in the deflator, because they are not domestic output. A rise in imported fuel prices lifts the CPI first.
• Weights. The CPI keeps a fixed basket for years at a time. The deflator's weights shift every year with the actual mix of output.
• Timing. The CPI is monthly and rarely revised. The deflator comes quarterly or yearly with GDP and is revised as national accounts are updated.

Because of these differences, a country can show deflator inflation well below or above its CPI inflation, especially when import prices, the exchange rate or export prices move sharply.

The PBS publishes Pakistan's national accounts at both current and constant 2015-16 prices, so the implicit GDP deflator can be read directly from its tables, and the Pakistan Economic Survey reports growth in real and nominal terms each fiscal year. Because Pakistan imports much of its fuel and machinery, its CPI and GDP deflator can diverge in years of large currency devaluation. The deflator is also the price measure that turns nominal values into real ones for figures such as Gross National Income (GNI).

Economists use the deflator to separate real growth from price growth, to compare price trends across countries, and to compute ratios such as tax-to-GDP and debt-to-GDP in a consistent way. Central banks look at it when judging overall price pressure for monetary policy, though most target CPI inflation.

Its limits are practical. It comes out late and is often revised; it does not show what households pay, so it is a weak guide to the cost of living or purchasing power; and its quality depends on the price indices and output data behind it. In economies with a large informal economy, missing output and prices can make both nominal and real GDP, and so the deflator, less reliable. When the deflator rises while real output falls, it is a sign of stagflation.

• U.S. Bureau of Economic Analysis: GDP Price Index
• Pakistan Bureau of Statistics: National Accounts