Why Low iROAS Is Normal (and Even Expected) for Top-of-Funnel Campaigns

When marketers test top-of-funnel (TOF) campaigns like YouTube, TV, or out-of-home (OOH), they often get nervous when incremental return on ad spend (iROAS) comes back “low.”

The truth? That’s normal, and it doesn’t mean the campaign is a failure.

At fusepoint, after running over 1,200 incrementality tests and thousands of models across industries, we’ve learned that low iROAS on TOF campaigns is both common and expected. 

What matters is understanding why it happens, how to set up your tests correctly, and how to interpret results in the context of long-term brand building.

Let’s break it down.

Before diving deeper, a quick refresher:

We also distinguish between:

Even though it might feel discouraging, lower iROAS on TOF campaigns makes sense, here’s why.

When you launch a net new channel, it doesn’t reach its full potential overnight. It takes time to:

This maturation process applies whether the channel is inherently TOF (like OOH) or just new to your mix (like TikTok or YouTube). You can’t fairly compare a new, immature channel to something like Meta or Search that’s been optimized for years.

Most incrementality tests run for 4–8 weeks, sometimes up to 12. But TOF campaigns don’t usually show their full impact that quickly, especially for high-consideration purchases.

Growth-oriented TOF tactics are designed to layer on top of existing performance channels, which means their impact is gradual and often delayed. We’ve seen campaigns where iROAS improves significantly after the test ends, sometimes doubling or tripling within 6 months.

For example:

Even Google and Ekimetrics found that in some verticals, only half of media impact happens in the first 5 months, with the rest accruing over months 6–24.

So how do you ensure your TOF incrementality tests give you actionable insights?

Don’t stop measuring when the campaign ends. Monitor iROAS well beyond the testing period to capture its full impact.

TOF campaigns work by building mental availability, which requires saturating your audience at meaningful R+F levels which is generally reaching at least 15% of your target audience in the affected geo, at a frequency of at least 2x per week across this audience.

Understand that some campaigns, especially for high-price or high-consideration categories, may take 12–18 months (yes, months!) to deliver their full ROI.

Here are the key lessons for marketers running TOF campaigns:

At fusepoint, we’re often satisfied when a test shows even a modest “floor” at 90% confidence, because it indicates positive momentum. For example, a YouTube test with a 90% CI iROAS range of $0.25–$1.50 is promising, and likely to grow over time.

Top-of-funnel media is critical for long-term brand growth, but it behaves very differently than direct response channels. As long as you structure your tests properly, set the right benchmarks, and measure over the right horizon, even a “low” iROAS at first can be a sign you’re laying the foundation for future success.

Want help designing a smarter TOF testing strategy? Reach out.