What is it?
Incrementality is the measure of additional value your product brings to a retailer's category - sales that wouldn't have happened without you on shelf. The opposite is cannibalisation: your product simply stealing sales from something already there. Cannibalisation bad, incrementality good. Now for the interesting stuff.
Why it matters more than your sales data
Buyers are judged on category performance, not brand performance. However strong your numbers are, they’ll almost always ask: "where are those sales coming from?" And if the honest answer is "mostly from the product next to us on shelf" you have a problem.
This is why leading with your own sales data alone is rarely enough. The good news: you don't need perfect data to make the incrementality argument - just a few sensible assumptions.
Putting a number to it
Context: You’re pitching a new energy drink, BUZZ. Your key target is women aged 25–40. In your target retailer, 500,000 women in this group shop soft drinks annually, but only 12% of those buy energy drinks. That leaves 440,000 soft drink shoppers who are not in the energy drinks category.
The numbers: If just 5% of those non-energy shoppers occasionally add BUZZ to their basket, that's 22,000 new category buyers. Assuming each buys 6–8 times per year at £3.00 per purchase, that's £396k–£528k in category sales.
Adjusting conservatively for cannibalisation within drinks gives an estimated £238k–£317k of true incremental value.
In practice:
"Based on recruiting just 5% of eligible non-energy shoppers already in your store, BUZZ could deliver around £240k–£315k in incremental category sales in year one, even after allowing for cannibalisation within the drinks aisle."
Using incrementality proactively
Most brands reach for incrementality when challenged. The smarter play is to use it proactively, to support your case to replace an existing product. If two products are serving an almost identical shopper, there’s a cannibalisation problem worth raising.
"Products A and B have an 80% shopper overlap. Replacing Product B with BUZZ protects existing sales whilst bringing an entirely new shopper to category. Net result: category growth."
Plant this seed before a ranging review and you'll be front of mind when decisions are made.
The bottom line
Incrementality is not about whether people buy your product - it’s about whether they buy more category because your product exists. To buyers, this is the gold standard.