GDP Deflator = (Nominal GDP / Real GDP) × 100
Nominal GDP = GDP measured at current prices
Real GDP = GDP measured at constant prices
Use the same base year prices for Real GDP
Divide Nominal GDP by Real GDP
Multiply the result by 100
The result is the GDP deflator index
A GDP deflator above 100 means prices have risen since the base year
A GDP deflator below 100 means prices have fallen since the base year