Price index: definition and calculation
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Do you know where your price index stands this week?
Schedule a meetingDiscover our pricing optimization softwareA price index measures a price level relative to a reference value of 100. In economics, this is the INSEE's Consumer Price Index (CPI), which tracks inflation. In retail, the competitive price index (or price index) compares your prices to those of your competitors for the same basket of goods: an index of 105 means you are 5% more expensive than the reference price.
The Essentials in 6 Questions
A 100-point index showing your price level relative to the market.
Pricing, management, purchasing, and marketing.
A weekly publication in a highly competitive market; a monthly elsewhere.
Based on a representative basket , by department and by channel if necessary.
To manage price competitiveness and quickly detect deviations.
Retail price ÷ reference price × 100 , product by product then aggregated.
Consumer price index or competitive price index: what's the difference?
Both are based on the same base-100 mechanism, but one compares dates, the other compares brands.
| CPI (INSEE) | Competitive price index | |
|---|---|---|
| What he compares | Today's prices compared to those of a base period | Your prices compared to those of one or more competitors, on the same date |
| Question asked | "By how much have prices increased?" | "Am I more expensive or less expensive than the market price?" |
| Basket | Total household consumption, weighted by expenditure | Your comparable products, often centered on KVI |
| Who calculates it? | INSEE, every month | The retailer or distributor, based on its records |
| What is it used for? | Measuring inflation, indexing contracts, pensions and minimum wage | Managing pricing positioning and price image |
The CPI published by INSEE is currently calculated using a 2025 base year (the 9th generation of the index, in effect since January 2026) and is published monthly in the Official Journal. It's the benchmark for tracking inflation, but it doesn't reveal anything about your position relative to your competitors. For a retailer or distributor, the price index most useful on a daily basis is the competitive price index , which is the subject of the rest of this page. It closely resembles the relative price , aggregated across a basket of goods and services.
Why the price index is the KPI of competitiveness
Because it summarizes your pricing position relative to the market in a single figure that the entire company can understand.
- Driving Competitiveness: A clear, data-driven view of your market position—essential for adjusting your pricing strategy.
- Track changes over time: Calculated weekly or monthly, it quickly reveals deviations and opportunities.
- Aligning teams : management, purchasing and marketing all include an index based on 100.
This is why it is at the top of the pricing KPIs and is used to measure the price image of a brand.
How do you calculate a price index?
We compare the price of the same basket at home and at the reference store, then we express it as a base of 100.
Select the basket
The KVI products and a representative sample of the product line.
Raise prices
At our store and at competitors' stores, including promotions.
Match the products
Same reference, or equivalent product for own brands.
Express as a subscript
(Brand price ÷ benchmark competitor price) × 100.
An index of 98 means you are 2% cheaper. Two methods exist: the basket ratio (your total ÷ competitor's total) and the average of ratios product by product, weighted by revenue or volume. The second method prevents a high-priced product from overshadowing all others and better reflects the actual customer experience. Competitor prices come from your competitor price surveys , and the quality of the matching depends on the product matching . Our price optimization software then continuously calculates the index and simulates the effect of each adjustment. See also: price gap and pricing positioning .
A concrete example: from 102 to 99 in one week
A retailer goes from being 2% more expensive to 1% cheaper than the average by adjusting the prices of 50 out of 200 products.
A targeted adjustment that shifts the entire index
A basket of 200 products, compared to 3 competitors
One-week price index, after adjusting 50 strategic components out of the 200 in the basket.
The retailer calculates its price index weekly based on 200 representative products, comparing them to its three main competitors. It then continuously monitors this indicator to maintain its "competitive pricing" positioning while preserving its overall profit margin.
Overall index, by radius or on KVI: which one to follow?
All three, because an overall index of 100 can hide an overpriced department and poorly placed loss leaders.
- Overall index : the direction view, to follow the trend and compare competitors with each other.
- Index by department or category : it shows where you are losing competitiveness and where you have room for maneuver.
- Key Value Index ( KVI) : the products whose price the customer remembers. This is what shapes perception, much more so than the overall index (see the halo effect ).
The 3 errors that distort a price index
A poorly chosen basket, forgotten promotions or a single multi-channel indicator give a misleading image.
- Basket not representative : an index based on 30 random products has no value; the basket must reflect actual purchases.
- Ignoring promotions : comparing prices displayed without current promotions skews the index.
- Single index for all channels : positioning may differ between web and store; calculate separate indices if necessary.
See also : Common Pricing Strategy Mistakes.
Frequently Asked Questions
Short answers to the most frequently asked questions about the price index.
What is the price index?
A price index measures a price level relative to a reference value of 100. The best-known is the INSEE's Consumer Price Index (CPI), which tracks inflation. In retail, this is called a competitive price index, or price index: it compares a retailer's prices to those of its competitors for the same basket of products.
What is a price index?
This is the ratio between a price and a reference price, multiplied by 100. If a product costs €2.10 at your store and €2.00 at the benchmark competitor's store, its index is 105: you are 5% more expensive on this product. Aggregated across a basket of goods, these indices form the retailer's price index.
What is the difference between the CPI and a competitive price index?
The CPI compares prices over the same period to a base period to measure inflation. The competitive price index compares your prices to those of your competitors at the same date to measure your competitiveness. Same base of 100, different question.
Where can I find price indices?
Official indices (CPI, HICP, producer price indices) are published by INSEE and Eurostat. A competitive price index is not published anywhere: each retailer calculates it from its own competitor price surveys, ideally using a tool that updates it continuously.
How to calculate a price index in the face of competition?
Note the prices of the same basket of goods at your store and at the benchmark competitor's store, calculate for each product the ratio of store price ÷ competitor price × 100, then take the average weighted by turnover or volumes.
Should out-of-stock products be included in the index?
No. If a competitor is out of stock on a product, it skews the comparison: temporarily exclude it or replace it with an equivalent product.
How often do you recommend performing the calculation?
Weekly for highly competitive markets such as food and electronics, and monthly for more stable markets such as home improvement and furniture.
Does the price index replace product-by-product analysis?
No, it complements it. The index provides a macro view; the analysis of gaps product by product identifies the precise levers for action.
Key Takeaways
- The price index measures a price level as a base of 100 : the CPI tracks inflation, the competitiveness index tracks your competitiveness.
- It is calculated on a representative basket , including promotions, product by product and then aggregated.
- Follow it globally, by department and on KVI , and supplement it with product-by-product analysis .
Would you like to track your price index compared to the competition?
Booper continuously calculates your price index based on the product basket that matters to your customers.
Let's talk about your price index →Discover our pricing optimization softwareYou might also be interested in these articles
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