6 Things You Need to Know About Incrementality

For years, marketers have relied on simple metrics like ROAS and CPA that are clean and easy to interpret. But there’s a problem: These metrics can’t tell you if your ad spend actually made a difference.

Incrementality asks the harder, more important question: Would this result have happened if we didn’t spend the money and invest in this channel? And answering that question is what separates “we got lucky” from “we made a great investment.”

The trouble with incrementality is that many marketers struggle to measure it accurately. A performance agency we spoke with reported that less than 1% of their brand clients had proper incrementality testing in place, leading to misallocated budgets of 10–30%. 

If you want to move beyond guesswork, here are six things you need to know.

Incrementality is a curve, not a number

More precisely and scientifically stated, incrementality is measured as a curve based off of the depreciating ad effect. The impact of an ad starts to decay immediately after it is seen.

When platforms report incrementality, they don’t always tell you when they’re measuring on the curve. Is it a 7-day window? 30? If you’re comparing across channels, this really matters.

This is especially painful for marketers because they usually want to know right away whether a campaign is going well. Did the new creative hit? Is this audience worth retargeting? Are we up or down this week? Incrementality doesn’t operate on that kind of instant gratification timeline.

You can’t tack incrementality onto a weekly campaign dashboard. By design, incrementality requires time, control groups, and a well-structured test. It’s less about what happened yesterday and more about answering, “Did this strategy actually make a measurable difference?”

The right question comes before the test

Here’s where many marketers go wrong: They rush to set up an incrementality test—control groups, creative, the whole nine yards—without ever asking what they’re actually trying to learn. It’s like building a laboratory before deciding whether you’re testing for the flu or baking cookies. Sure, you might get data that looks impressive, but if you don’t answer the business question leadership actually cares about, what’s the point?

Let’s say you’re trying to answer, “What’s the impact of this channel on our overall growth strategy?” That’s a broad, long-term question, which requires a universal holdout test that runs over time and captures the collective effect of your channel strategy. It’s a zoomed-out, strategic view.

But if you’re asking, “How did this one campaign perform against its control group?”, that’s a campaign-level test, and it’s all about the here-and-now. It’s narrower, more tactical, and focused on short-term lift that can inform creative and offer testing.

Both are valid questions, but they require different methodologies, different audiences, and different timeframes.

You can’t stitch together campaign-level results and call it a strategy

We see this mistake all the time: Marketers run multiple campaign-level incrementality tests and then try to average the results into some kind of channel-level insight. On paper, it feels logical—stack up a few lifts, do a little math, boom: strategy. But in practice? It doesn’t work.

Why? Because each campaign-level test is measuring a different audience at a different moment in time, under different conditions. One campaign may target first-time buyers in spring. Another might focus on lapsed customers during the holiday season. Even if they’re both technically running in the same channel, they’re measuring different things. Trying to average them out is like blending apples, oranges, and pineapples and calling it a banana. It’s a fruit salad, not a conclusion.

If your goal is to understand the overall impact of a channel, you need a universal holdout test. This means creating a single, consistent control group—ideally drawn from the pool of people you expect to target over the full campaign timeline—and then measuring performance across all campaigns against that same group. That’s how you capture real, comparable, channel-level lift.

There’s no such thing as a ‘single-channel consumer’ anymore

Unlike the story of a Peruvian tribe discovered in 2024 with no prior outside contact, there’s no segment of U.S. consumers who are only reachable through a single marketing channel. This means that the desire some marketers have for each new paid channel to only bring in net incremental consumers is not realistic. 

When you’re measuring the lift from your Meta campaigns, for instance, you’re not measuring it in a vacuum. Those same consumers are likely seeing your YouTube ads, scrolling past your email, or receiving your postcards in the mail. This omnipresent media environment means that incrementality is increasingly about channel interaction, not just isolated performance. 

Marketers must not expect to find the consumer version of the Peruvian tribe—a purely incremental group of buyers never reached before by paid media.

Don’t chase high incrementality—find your Goldilocks zone

It’s tempting to look at a high incrementality number and say, “Let’s put all our budget there.” But that’s not strategy—that’s tunnel vision.

Smart marketers look for balance. If one channel is doing all the heavy lifting while others lag behind, it’s not time to cut the weak links. It’s time to investigate. The point is to balance the entire mix—not just overfeed the strongest performer.

Don’t optimize for incrementality … cuz ya can’t

Yet another hard truth: You shouldn’t “optimize for” incrementality in isolation. It’s not a leaderboard, it’s a diagnostic tool—meant to inform your strategy, not dictate it.

Yes, in theory, you could juice your incrementality number by only targeting people least likely to convert. Any conversion in that group will look incredibly “incremental.” But in doing so, you’d likely tank your revenue, experience high CPAs, and spend a whole lot of budget on low-probability bets.

That’s why we caution against using incrementality as a goal in and of itself. It’s not something to maximize. 

Instead, treat incrementality as a directional signal. It’s your early warning system for waste—or opportunity. Is your spend still driving lift, or are you seeing diminishing returns? Is a certain channel tapped out? Is another performing above expectations? These are the questions incrementality helps you answer—not, “How do I crank this number up?”

Incrementality is helpful only if you use it correctly

The most thoughtful marketers we work with don’t chase the highest ROAS, lowest CPA, or highest incrementality. They chase the most efficient growth, with incrementality increasingly helping them know where and how to reallocate budget for the biggest impact.

Think of incrementality like a compass—not a scoreboard. It won’t tell you if you’re “winning,” but it will help you stay on the right path.