What is the Price Index: Definition & Calculation

By Thomas Bennett Financial expert at Priceva
Published on November 23, 2022
In order to thrive and outperform their competitors, e-Commerce businesses need to keep tabs on pricing and optimize the cost of their goods. The price index allows for making a more detailed and accurate analysis of prices both on your shelves and those of your competitors. This guide explains what the price index is, how to calculate it and use it in your financial strategy.

What Is CPI?

The Consumer Price Index (CPI) is a measure that examines the weighted average of prices of a basket of consumer goods and services, such as transportation, food, and medical care. It is calculated by taking price changes for each item in the predetermined basket of goods and averaging them. Changes in the CPI are used to assess price changes associated with the cost of living; thus, it is one of the most frequently used statistics for identifying periods of inflation or deflation.

What is the Price Index (PI) Used for in eCommerce?

In the realm of eCommerce, the Price Index (PI) serves as a crucial metric for benchmarking a business's pricing strategy against its competitors. It provides an insightful glimpse into the pricing landscape of the market, revealing how a company's product prices stack up against those of its rivals. By analyzing the Price Index, eCommerce businesses gain a deeper understanding of the competitive dynamics, including who commands the largest market share and under what pricing conditions they operate.

The process of monitoring the Price Index involves a thorough examination of competitors' product assortments, employing a specific formula for the Price Index calculation, and analyzing historical sales data. This rigorous analysis helps eCommerce operators to discern market trends, detect pricing fluctuations, and adjust their strategies accordingly. Armed with this knowledge, businesses can strategically position their pricing, optimize their product offerings, and enhance their market competitiveness. Understanding the Price Index, alongside other economic indicators such as the Consumer Price Index (CPI), inflation rates, and purchasing power, equips eCommerce entities with the data needed to make informed decisions that align with market demands and economic conditions.

Price Index Calculation

Let’s go over several formulas used to calculate the exact price index for each product and average price index for several competitors.

To start with, you need to calculate the price index for each product or each competitor. This is done by dividing the cost of a competing product by the cost of your own item:
To calculate the average price index on the market, divide the sum of calculated price indices by the number of competitors:

How Exactly to Calculate the Price Index?

In order to get accurate price index calculations, follow the steps below:

  1. Collect relevant pricing data. The more competitors you want to compare, the more time you will have to spend on manual work, so make sure to use reliable monitoring tools. In some markets, prices should be monitored daily, otherwise you risk dealing with outdated prices or competitors that no longer exist.
  2. Make a single spreadsheet with all the pricing data you collect. It should be properly structured and easily available for you to operate it seamlessly.
  3. Use formulas from the previous paragraphs. Adding data gathered in your spreadsheet should not be a problem – you can fetch information from MS Excel in a few clicks.
  4. This point is optional but it wouldn’t hurt to visualize the data – you will be able to see market tendencies and compare competitors’ sales results.
  5. Fetch all your sales data. Analysis of price index would be useless without sales data because it tells you what market impact your competitors have.
  6. Find out what affected your sales. Armed with all this information, you can figure out how price changes affected buyers' purchasing decisions.

Complexity of Calculation

At first glance, doing all the calculations using the above-mentioned formulas is an easy task. However, you should be prepared to run into some issues.

The major problem that you might face is data accuracy. Some companies make a mistake by getting information on marketplaces instead of from rival websites directly – these numbers may differ significantly.

Other eCommerce businesses use their own parsers or obtain pricing information manually. But since our concentration lasts up to a few hours, the risk of human error is pretty high. Irrelevant data can lead to wrong pricing decisions.

Even if you manage to achieve impeccable data quality, it’s only half the battle – you must also process and analyze the information. Human errors can occur when a person compares figures or tries to figure out a repricing strategy.

How to overcome this problem? Automation is the answer. Consider integrating repricing tools and price optimization software: it will track prices on competitor websites and marketplaces, analyze pricing history and provide recommendations on optimal price points. You can get real-time price index data by adding your formulas to a software dashboard – no manual calculations required.

How Can the Price Index Affect Your Pricing Strategy?

Essentially, the price index serves to show the direct relationship between prices for the same item or service. It can also be applied to analyze the whole lineup to see how your business stands out from the crowd of your competitors.

How exactly can these numbers be used in your business? By analyzing price fluctuations and sales volumes at those moments, you can draw the conclusions concerning the way price impacts demand. With this data at your fingertips, you can make predictions about sales of certain goods and predict the market’s reaction to such price changes.

As we’ve mentioned, price tracking software is here to help: it will analyze pricing data and sales statistics for you to make an in-depth competitive study. Just choose the metrics you want to research and don’t forget that price indices can be calculated automatically. Priceva software can also generate recommendations or even update your prices routinely – that’s a great feature for businesses that need price updates several times a day.

How to Adjust Your Pricing Strategy with the Price Index

Price index data will enable you to build a more efficient pricing strategy based on both competitor and market analysis. The key point here is to identify market ups and downs and adjust your prices in a way that allows you to sell more.

For example, you will be able to catch the moment when your competitors reduce prices or when they are selling off the remaining stock from their warehouses. That will allow you to understand what drives price fluctuations and be prepared for different situations that occur on the market.

In short, the price index helps you to adapt smarter and quicker by seeing what price points work better at certain moments. You get better control over your pricing strategy and can predict great profit generating opportunities.

Examples of Calculating CPI Formula

Calculating the Consumer Price Index (CPI) involves a detailed process that tracks the price changes of a "market basket" of consumer goods and services over time. The CPI formula can be summarized as follows:

CPI=Cost of Market Basket in Base Year/Cost of Market Basket in Current Year)×100

To elucidate, let's consider a simplified example:

Example 1:
Assume the base year is 2010, and we're calculating the CPI for 2020. The market basket consists of three items: bread, milk, and gasoline.

  • In 2010 (Base Year), the prices were: Bread = $2, Milk = $3, Gasoline = $2 per gallon. The total cost of the basket = $7.
  • In 2020 (Current Year), the prices changed to: Bread = $3, Milk = $4, Gasoline = $3 per gallon. The total cost of the basket = $10.
Using the formula, the CPI for 2020 would be calculated as:

CPI 2020=(10/7)×100=142.86

This indicates that the price of the market basket has increased by 42.86% from 2010 to 2020.

Example 2:
For a more comprehensive understanding, consider the CPI calculation involving a weighted average, which accounts for the relative importance of items in the basket:

Assuming the weights for Bread, Milk, and Gasoline are 30%, 20%, and 50% respectively, and using the prices from the previous example:

  • The weighted cost in the base year would be: $2(0.30) + $3(0.20) + $2(0.50) = $2.10.
  • The weighted cost in the current year would be: $3(0.30) + $4(0.20) + $3(0.50) = $3.10.
Applying these to the CPI formula:

CPI weighted=(3.10/2.10)×100=147.62

This method reflects how the average price change affects the cost of living by considering the differing importance of items in the consumer's budget.

The Importance of Price Index

The Price Index, particularly the Consumer Price Index (CPI), serves as a critical economic indicator, offering insights into the health and direction of an economy. Its importance cannot be overstated for several reasons:

Inflation Measurement
The CPI is pivotal in measuring inflation rates. By tracking the price changes of a market basket of goods and services over time, the CPI provides a clear picture of how the cost of living is evolving. This is crucial for both consumers and policymakers to understand the purchasing power of money and how it changes.

Purchasing Power
The CPI directly impacts the purchasing power of consumers. As prices rise (inflation) or fall (deflation), the amount of goods and services that can be purchased with the same amount of money changes. Understanding this dynamic helps in adjusting wages, pensions, and social security benefits to maintain living standards.

Monetary Policy
Central banks, like the Federal Reserve System in the United States, use the CPI as a guide to adjust monetary policy. By targeting specific inflation rates, they aim to control economic growth, manage employment levels, and stabilize the currency. Adjustments to interest rates are often made based on CPI data to curb inflation or stimulate economic growth.

Economic Analysis and Planning
Businesses and governments rely on CPI data for economic planning and forecasting. The CPI's insights into consumer spending trends and price changes help in making informed decisions regarding production, pricing strategies, and fiscal policies.

Adjustment of Contracts
Many financial contracts, including bonds, leases, and salaries, contain clauses that adjust payments based on CPI movements. This ensures that the value of the payments remains fair and relevant despite inflationary changes.


The price index is the metric that shows how your goods or a category of goods are positioned on the market. It can be calculated using the above-mentioned formulas or with the help of repricing software that automatically gathers pricing information. By using the price index you can take a peek into competitor tactics, make data-driven decisions and keep your price points at an optimal level.


What is the price index in simple words?

The price index is the metric that shows the difference in price between your and competitors’ prices for one and the same product. It also indicates a measure of the proportionate, or percentage, change in a set of prices over time.

What is the price index example?

One of the price indices is Consumer Price Index (CPI) – it shows price changes in a basket of consumer goods or services, and averages for each position.

What is a normal price index?

This is a relative metric that varies depending on the market niche, period and many other factors. The price index itself is a normalized average of price relatives for certain items or services during a certain interval of time.

More to explore