Price Index/GDP Deflator:

Price Index: measures inflation by tracking changes in the price of a market basket of goods compared to the base year.

Price of market basket of goods in current year - Price of market basket of goods in base year X 100

GDP deflator = price index that is used to adjust from nominal to real GDP.

In the base year, the GDP deflator will equal 100.
 For years after the base year, the GDP deflator will be greater than 100. 
For years before the base year,  GDP deflator is less than 100. 

Inflation: new GDP deflator - old GDP deflator / old GDP deflator X 100.