GDP Deflator vs Real GDP
GDP Deflator and Real GDP are two Measuring the Economy concepts in AP Economics that students often mix up. The GDP deflator is a measure of the level of prices of all new, domestically produced, final goods and services in an economy. Real GDP is the value of all final goods and services produced in a given year, evaluated at base-year prices to remove the effects of inflation. Here is how they compare side by side.
It is calculated as the ratio of nominal GDP to real GDP, multiplied by 100, and shows how much prices have changed since the base year. It is a broad measure of inflation that includes all goods and services in GDP, unlike the CPI which uses a fixed basket.
It measures actual changes in output by holding prices constant, allowing for accurate comparisons of economic growth over time. Real GDP is the preferred measure for analyzing long-term economic trends and productivity.
GDP Deflator vs Real GDP: Separating the Price Tag From the Quantity
| GDP Deflator | Real GDP | |
|---|---|---|
| What it measures | The price level of everything a country produces | The quantity of output, valued at base-year prices |
| Units | An index number with the base year set to 100 | Dollars |
| Formula | Nominal GDP divided by real GDP, multiplied by 100 | Nominal GDP divided by the deflator, multiplied by 100 |
| Value in the base year | 100 by definition | Equal to nominal GDP for that year |
| What a rise means | Domestically produced output costs more than before | More goods and services were actually produced |
| What it is used for | Calculating inflation between two years | Calculating growth, and comparing output across years |
| What it cannot tell you | Nothing about how much was produced | Nothing about what happened to prices |
The two are linked by one identity, so any two of the three numbers give the third
Nominal GDP, real GDP and the deflator are bound together: the deflator equals nominal GDP divided by real GDP, multiplied by 100. Take an illustrative economy where nominal GDP is 660 billion dollars and real GDP, valued at base-year prices, is 600 billion dollars. The deflator is 660 divided by 600, multiplied by 100, giving 110. Prices of domestic output are 10 percent above the base year. Rearrange the same identity to go the other way: real GDP is 660 divided by 110, multiplied by 100, which returns 600 billion dollars. Now run the economy forward. Nominal GDP rises to 726 billion dollars and the deflator rises to 121. Real GDP is 726 divided by 121, multiplied by 100, which is 600 billion dollars again. Nominal output grew 10 percent and the country produced not one extra unit, because the deflator also rose 10 percent, from 110 to 121. That is the whole reason the pair exists. One number carries the prices, the other carries the quantities, and the nominal figure blends the two so completely that it cannot be read on its own. Practice conversions are at /calculate/gdp-deflator.
The deflator is not the CPI, and the differences change the answer
Both are price indexes, and a question that hands you one when you expected the other is testing whether you know the coverage. The deflator covers everything counted in GDP, meaning all final goods and services produced inside the country, including machinery, government services and exports. The consumer price index covers a fixed basket of goods a typical household buys, which leaves out capital equipment and includes imported consumer goods that the deflator excludes. The weighting also differs. The consumer basket is held fixed for long stretches, so the index keeps asking what an unchanged shopping list costs, while the deflator reflects whatever the country actually produced in the year being measured, so its composition shifts on its own. A sharp rise in the price of imported oil pushes the consumer index up quickly for an oil-importing country while touching the deflator far less. Neither is the true rate of inflation, since both answer slightly different questions. For growth, real GDP is the measure to use, since it holds prices at base-year levels and lets the quantity move, as shown at /calculate/real-gdp.
Frequently asked questions
How do you calculate the GDP deflator?
Divide nominal GDP by real GDP and multiply by 100, so nominal output of 660 billion dollars against real output of 600 billion dollars gives a deflator of 110. The result is an index rather than a dollar amount. A value of 110 means prices of domestically produced goods are 10 percent above their base-year level.
Is a rising GDP deflator the same as rising real GDP?
No, a rising deflator means output is being sold at higher prices while rising real GDP means more output is being produced, and the two frequently move in opposite directions. Nominal GDP can climb steeply while real GDP is flat if the whole increase came from prices. Separating those two stories is the point of having both numbers.
Why is the GDP deflator 100 in the base year?
The deflator is 100 in the base year because real GDP is calculated using base-year prices, so in that one year nominal and real GDP are identical and their ratio is exactly 1. Multiplying by 100 turns that ratio into an index. Every other year is then read as a percentage of base-year prices.
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