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What Are Price Index and Consumer Price Index?

A price index describes the relationship between the price of a product one year and the price of that product in a base year.

A price index enables us to calculate the change in price over time, or between different parts of the world. It is important to remember that the price index in the chosen base year is 100.

Formula

Price Index in Relation to Base Year

Price index = price price in base year 100

Formula

Price Index in Relation to Any Year

price index 1 price index 2 = price 1 price 2

Example 1

The base year price of an item was $9.80. In 2015, the price index was 235. What was the price of the item in 2015?

The price index of the base year is always 100. You can just insert the given information into the formula, which will give you price index 2015 price index base year = price 2015 price base year 235 100 = price 2015 9.80 235 100 9.80 = price 2015 9.80 9.80 price 2015 = 235 100 9.80 = 23.30

The price of the item was $23.30 in 2015. That means the value of $1 has decreased, and stores have raised the price for the same item to compensate.

The consumer price index (CPI) takes various price indices for a number of products and averages them. It is intended to approximate how the whole market has changed in price each year. It’s very useful when calculating inflation and when you negotiate salaries.

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