The Incrementality of Prime Day
What Jeff’s Wedding and Prime Day Have in Common

(Spoiler: Too Much Spend, Not Enough Return)

Prime Day 2025, Amazon’s annual mega-event, landed with predictable noise: deep discounts, aggressive promotions, and a firehose of paid media. But the real circus? That was in Venice, where Jeff Bezos and Lauren Sánchez threw a wedding that reportedly cost somewhere between $20 million and $56 million. There were water taxis, black-tie billionaires, designer gowns, and a multi-day spectacle that would make a Roman emperor blush.

While the cameras were glued to Bezos and company, advertisers were glued to dashboards. With billions in global ad spend hitting the market, Prime Day has become more than a shopping event. It's a test of strategy, scale, and sanity.

What Went Into the Analysis

Using INCRMNTAL’s AI-driven measurement platform, we analyzed campaign data across fintech, ecommerce, DTC, and mobile apps during Prime Day 2025. The window was July 8 to 11. The sample included millions in verified ad spend and thousands of incremental installs.

Unlike attribution tools that guess based on clicks or impressions, INCRMNTAL measures actual lift. We isolate what worked, what moved the needle, and what just looked good on a dashboard.

For anyone serious about incrementality in marketing, this approach reveals what attribution often hides.

1. Prime Day performance shifted faster than most campaigns could react

Spend held steady in many cases, but results didn’t. ROAS and CPA swung wildly day to day. This wasn’t about creative fatigue or platform quirks. It was about external demand shifting faster than most media strategies could.

That’s where AI in data analysis proves its worth, spotting change in real time, not after it’s too late.

Takeaway: If your campaign plan can’t flex by the hour, it’s not built for Prime Day.

2. Small budgets delivered big results

The highest ROAS wasn’t from the biggest spenders. Advertisers with sub-$5K daily budgets often outperformed large-scale campaigns. Smart targeting and sharper focus made the difference.

Takeaway: Precision beats volume when the market is crowded.

3. Scaling without strategy torched efficiency

Several advertisers ramped up spend thinking Prime Day would take care of the rest. It didn’t. Installs stalled. CPA went up. ROAS dropped hard.
This wasn’t a creative issue or audience fatigue. It was saturation. More money entered the auction while demand didn’t grow fast enough to meet it. Without adjusting bids, pacing, or placements, spend became waste.

 

Takeaway: More budget only works when the market wants more of you.

4. Attribution overestimated real impact

Standard attribution tools made a lot of campaigns look great. But INCRMNTAL’s analysis showed something different. In many cases, the “lift” was minimal or nonexistent. 

This is exactly why teams need a reliable marketing data analyst to validate performance beyond surface-level metrics.
Attribution handed out credit. Incrementality showed who actually deserved it.

Takeaway: Prime Day exposes the gap between visibility and value.

5. Spend went up while returns stayed flat

In several cases, advertisers increased spend across the four days and got little in return. Incremental installs barely moved. The marginal cost of growth kept climbing.

This wasn’t surprising. Demand has limits. Ad auctions don’t.

Takeaway: Without new demand, scaling just raises your burn rate.

Final Thoughts…

Prime Day rewards strategy. It punishes complacency. It exposes how much of your performance is real and how much is propped up by flawed measurement.

Attribution tells you what happened. Incrementality tells you what mattered.

Bezos threw an expensive party. Advertisers threw expensive campaigns. One got married. The other got tested.

If you're not measuring lift, you're flying blind.