If you only look at one number in retail media, most people tell you to look at ROAS — return on ad spend. It’s simple, it’s everywhere, and it’s often misleading. The number that actually matters is incrementality: how much of your sales the advertising truly caused. Here’s the difference and why it matters.
What ROAS measures
ROAS is just attributed sales divided by spend. Spend $1,000, drive $4,000 in attributed sales, and your ROAS is 4. It tells you how much revenue the platform credited to your ads relative to what you paid. Useful as a gut-check — but it has a blind spot.
The blind spot: sales you’d have had anyway
Here’s the trap. If you bid on your own brand name, or on shoppers already loyal to you, your ROAS looks fantastic — because those people were going to buy you regardless. You paid to take credit for sales you already had. High ROAS, near-zero real growth. It feels like winning while the business doesn’t actually move.
A gorgeous ROAS on shoppers who’d have bought you anyway isn’t growth. It’s paying for sales you already owned.
What incrementality measures
Incrementality asks the better question: of the sales attributed to your ads, how many are new — sales that wouldn’t have happened without the ad? That’s the number that reflects real growth. It’s harder to measure precisely, but you can reason about it: are you reaching new shoppers and new searches, or just re-buying your existing customers?
How to think about it practically
You don’t need a data-science team. Watch total sales, not just ad-attributed sales — is the whole business growing, or just the slice you’re paying to claim? Be skeptical of a soaring ROAS on tiny, brand-defensive spend. And favor campaigns that reach genuinely new demand — new keywords, new shoppers, new retailers — over ones that just harvest people already headed your way.
The goal
The aim isn’t the biggest ROAS. It’s the most incremental product moved at a price that still makes you money. Chase real growth, not a flattering ratio.
Want an honest read on whether your ad numbers reflect real growth or just recycled sales? A free shelf check gives you a straight look — in plain English.