Promotions: Measuring Incremental Revenue, not the volume displaced
A promotion that drives higher sales volume does not necessarily create more value: part of that volume already existed. Promotions now account for 21.9% of FMCG revenue in 2025, a 20-year high (NielsenIQ). Black Friday 2025 highlighted the gap between volume and value on a national scale: +0.4% in value, -3% in volume (Joko). Measuring this incremental impact on a product-by-product basis is the purpose of BOOPER’s Promotion Management module.
A promotion that generates twice as much sales volume does not necessarily create twice as much value. Part of that volume already existed: customers who would have bought the product anyway, a little sooner or a little later, at another store, or as a similar product.
This guide explains how to distinguish between truly incremental sales and sales that have simply shifted, and how to measure that difference without a complex testing lab.
The volume trap that hides the real issue
In most sales teams, a promotional campaign is judged by a single metric: the volume sold during the period. The higher the sales, the more successful the campaign is considered to be.
This assumption raises a simple problem: total volume says nothing about what the promotion actually generated. Of the 100 units sold during the promotion, some would have been purchased anyway, others were simply bought earlier than planned by customers who stocked up, and still others came from a nearby store of the same chain or a competing product in the same aisle. What remains, once these portions are accounted for, isthe actual increment —the only part that economically justifies the cost of the promotion.
Celebrating gross volume is tantamount to confusing shifted revenue with growth. It is precisely this bias that explains why a promotion can show a dramatic increase in sales while, at the same time, eroding margins over the entire period.
Incremental vs. Offset: The Distinction That Changes Everything
Incrementality measures the portion of sales that would not have occurred without the promotion —neither on that date, nor in that store, nor for that product. Everything else is shifted volume: it already existed somewhere in the system; the promotion simply brought it to light at a different point in the schedule or on the shelf.
A sale created
A customer who would not have purchased this product at that time without the offer — new net revenue.
A sale moved up or postponed
A purchase that would have taken place anyway, but was simply brought forward or postponed.
This distinction is not merely theoretical: it determines whether the cost of the discount offered is a profitable investment or a pure loss disguised as commercial success.
The 3 Leaks That Inflate Volume Without Creating Value
The non-incremental volume of a promotion can be broken down into three distinct mechanisms, each of which must be examined separately to understand where value is actually being lost.
| Leak | Mechanism | How to limit it |
|---|---|---|
| Deferred Purchase | Regular customers make their purchases or stock up when a sale is on, and then don't buy anything for several weeks. | Track sales over a broader period after the promotion, not just during it. |
| Store Report | A customer switches to a different store within the same chain to take advantage of the offer, without making any additional net purchases. | Compare sales at the store running the promotion with those at neighboring stores of the same chain. |
| Intra-category cannibalization | The promoted item captures sales that would otherwise have gone to a similar variant or format in the same aisle. | Measure sales trends for the entire category, not just the promoted item. |
A fourth type of customer loss, which is rarer but still real: customers switching from a competing brand to yours. This is the only one of the four that’s positive for you—but negative for the industry as a whole.
Our article on cross-elasticity, cannibalization, and the halo effect details the statistical mechanism behind the third leakage.
Black Friday 2025: Massive Sales Volume
This is not a minor issue, and the 2025 Black Friday event brought it to the nation’s attention. During Black Week, from November 21 to December1, 2025, the French spent slightly more than they did in 2024, but they bought fewer items.
in volume purchased during Black Week 2025, with spending up by only 0.4% in value. 62% of shoppers were getting a head start on their Christmas shopping (Joko, Black Friday 2025 report, as reported by FashionUnited on December 10, 2025).
In other words, a large portion of the demand captured during the promotion would have been purchased a few weeks later, often at full price. This is the purchase deferral described above, measured this time across an entire market. At the retailer level, the same phenomenon plays out on a product-by-product basis: without measuring incremental sales, it’s impossible to know which promotions generated sales and which merely brought them forward by offering a discount.
The record number of graduates in France in 2025
This observation takes on particular significance at a time when promotions are playing a more significant role than ever in the French retail sector. After two years marked by high inflation followed by a trend toward disinflation, retailers have made promotional offers a key strategy for maintaining their appeal.
of FMCG sales in hypermarkets and supermarkets came from promotional sales in 2025 —a record share over the past 20 years. At the same time, 45% of French households now report trying to buy on sale, up 2 percentage points (NielsenIQ, 2025 FMCG Market Outlook, report published in 2026).
The larger the share of revenue accounted for by promotions, the more critical it becomes to measure their actual incremental impact: at this volume level, even a few points of measurement error represent significant margin amounts, which accumulate week after week across the entire network.
Measuring Incremental Systems Without a Test Lab
Measuring incremental impact does not require the resources of a marketing research lab. Three approaches—which can be combined—are sufficient to obtain a reliable estimate: a control store or area that does not receive the promotion and serves as a benchmark; an extended measurement window before and after the campaign to detect deferred purchases; and an analysis at the category level to isolate intra-category cannibalization.
These three analyses require detailed, granular sales history—by SKU, by store, by week—and an elasticity model capable of calculating a credible baseline: what would have been sold without the promotion. Without this baseline, any measure of incrementality remains nothing more than a rough estimate.
Understand the impact before committing to the promotional budget
GENIUS Predict calculates a sales baseline by SKU and by store, then simulates the expected impact of a promotion on demand and inventory before its launch, taking into account cross-elasticities and cannibalization effects already identified within the category.
GENIUS Promotions then manages the execution of the campaign according to the defined business rules, while GENIUS Monitoring tracks in real time any discrepancies between the projected sales trajectory and actual sales.
Learn more about the platform on our MPS page : Booper, the modular pricing solution.
How many of your promotions are actually profitable?
Spend 30 minutes with our team to objectively assess—with supporting data—the truly incremental impact of your promotional calendar.
FAQ
Incrementality measures the portion of sales generated during a promotion that would not have occurred without it. The rest of the volume—often the majority—consists of sales that already existed elsewhere, either before or after the promotion, or at a competitor’s store.
By comparing actual sales to a baseline (what would have been sold without the promotion), and then isolating the shift in purchase timing, the shift in store choice, and intra-category cannibalization. The amount that exceeds these components is the actual increment.
This is because most campaigns are evaluated based on sales volume, without measuring the truly incremental portion. Black Friday 2025 illustrates this: spending increased by 0.4% in value terms, while sales volume declined by 3% (Joko). The promotion itself isn’t the issue—it’s the lack of measurement.
No. No promotion is ever 100% incremental. The goal is to determine where each campaign stands in order to make informed decisions, not to reach a theoretical threshold.
The most accessible method remains the store or test area, combined with its own sales history and an elasticity model to calculate a reliable baseline.
Cannibalization is one of the causes of non-incrementality, not the other way around: the volume taken from a neighboring SKU in the same store. Purchase deferral and store deferral are two other distinct causes.
Also in this series
- Cross-elasticity, cannibalization, halo effect
- Sales on Fresh Organic Produce: When a Good Promotion Cannibalizes Your Sales
- Pricing simulation: testing your pricing strategy
- Markdown: clearing inventory
- Calculating Sales Margin: The Complete Guide
Sources: Joko, Black Friday 2025 Report, as reported by FashionUnited (December 10, 2025) · NielsenIQ, 2025 Consumer Goods Market Report, published in 2026 · Booper, internal product data (GENIUS Predict, GENIUS Promotions, GENIUS Monitoring)
Further reading
A manufacturer that raises its list price does not set the price on the shelf. Between the negotiated list price and the displayed price lie the retailer, its markup, and its promotions. What is measured is the price elasticity of each product, retailer by retailer.
The volume sold during a promotion does not indicate whether it created value: part of it comes from similar products (cannibalization), and another part from purchases that were simply brought forward.
Each promotional scenario must be costed out prior to launch using the same metrics: base sales, actual incremental sales, cannibalization, carryover, halo effect, net margin for the category, and cost per unit actually gained.
Margin-volume arbitrage can then be explained: a stated objective, visible forecasting factors, constraints adhered to, and a documented validation process.
A national food retailer with more than 1,700 stores and several million price points per year: With Booper, its pricing teams simulate the impact of each decision on margins, competitiveness, and price perception before implementing it.