Seasonal sales surges don’t mean your ads worked. INCRMNTAL shows why promo-day spikes mislead marketers—and why incrementality, not attribution, reveals real impact.
For brand marketers, retail promo days like Black Friday, Singles’ Day, and Prime Day can feel like unmissable opportunities. The industry narrative is always the same: spend big, stand out, and ride the sales spike.
But here’s the uncomfortable truth: just because sales rise doesn’t mean your ads caused it.
At INCRMNTAL, we’ve analyzed more than $2 billion in verified ad spend across retail, gaming, fintech, and DTC brands—much of it tied to seasonal campaigns. And time and time again, we find the same pattern: performance looks excellent on paper, but actual incremental lift is far harder to find.
Take Prime Day 2025. Across fintech, E-commerce, and app marketers, we saw dramatic swings in ROAS and CPA—sometimes day-to-day—even when spend held steady. Some of the highest returns came from advertisers spending under $5,000 per day, while those who ramped up aggressively saw plateauing installs and diminishing returns. Standard attribution painted a rosy picture, but incrementality revealed the truth: many campaigns were riding the wave, not driving it.
And that’s hardly unique to Prime Day. The bigger the shopping moment, the easier it is to confuse correlation with causation.
Promo Days Don’t Guarantee Performance
Advertisers often enter sales periods convinced that more spend will automatically translate into more results. It’s understandable: when your board expects a Q4 spike, it feels safer to follow the herd than test assumptions.
But what we consistently see is that seasonal demand does much of the heavy lifting without paid media. If consumers are already primed to buy, some of your best results may happen with or without your campaign.
And when everyone is bidding aggressively in crowded auctions—especially on platforms like Amazon—costs spike quickly. That’s a dangerous place to be without real-time visibility into what’s working and what’s waste.
Scale Isn’t Strategy
One of our biggest takeaways is this: precision beats scale.
Smaller, targeted campaigns often drive stronger incremental performance than large, broad bursts. Promo days attract intent-rich audiences—you don’t need to shout to be heard.
At the same time, spend is spreading across more channels than ever: CTV, influencers, DOOH, retail media, and more. While diversification brings opportunity, it also creates more surface area for misattribution. Without robust measurement, brands risk rewarding the loudest channels, not the most effective ones.
Attribution ≠ Impact
Promo days create the perfect storm for flawed attribution. Spikes in conversions often get credited to whichever ad was last seen, regardless of whether it actually moved the needle.
The result?
Platforms look like heroes.
Budgets shift based on incomplete data.
Inefficiencies snowball into the next quarter.
Incrementality measurement cuts through this. It reveals the real effect of your spend—not just what happened, but what wouldn’t have happened without your ads. That’s the metric marketers need when CPMs surge and budgets are on the line.
Three Principles for Promo Season 2025 and Beyond
With Black Friday, Cyber Monday, and January Sales ahead, marketers can approach seasonal campaigns more strategically:
- Measure continuously, not just after the campaign.
Always-on incrementality lets you adjust spend mid-flight and avoid pouring money into saturated markets.
- Don’t mistake demand for campaign success.
A conversion spike doesn’t mean your ads drove it. Focus on lift, not volume.
- Use seasonal insights to inform long-term planning.
Promo season learnings should shape evergreen strategy. Don’t scale what looked good—scale what actually worked.
What’s Next for Seasonal Performance?
Seasonality isn’t going anywhere—it’s getting more complex. Micro-moments like flash sales, influencer drops, and even weather-driven shifts now shape real-time purchase behavior.
That means performance marketing needs a rethink. You can’t rely on last-click attribution or platform-reported ROAS to guide decisions. And you definitely can’t assume that promo day conversions equal success.
Marketers must move from chasing spikes to understanding their causes. The key is embracing privacy-safe, always-on measurement approaches that reveal true drivers of performance—especially during high-pressure shopping periods.
The best campaigns of 2025/26 won’t be the loudest. They’ll be the ones powered by insights that show what’s really driving results—not just what happens during the spike.
