Run a native Conversion Lift study inside Google Ads, and the dashboard will almost certainly tell you that your campaigns drove a 35% to 50% relative lift in conversions. Your leadership celebrates, your agency claims victory, and you increase your daily budget by $10,000. Thirty days later, your overall company bank balance has not moved. Your total blended revenue is flat, yet Google insists that half your sales would not exist without your upper-funnel YouTube and Demand
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Google AdsHigh Impact
The Flaw in Google Ads Incrementality Testing That Inflates Your ROAS by 40%
Google's native conversion lift studies promise true incrementality, but cookie decay and Smart Bidding bias inflate lift by up to 40%. Here is how to fix it.
September 4, 20261 min readPublished by Gamal Hemdan
What This Means for Your Account
This update directly affects your campaigns.
Check your active Google Ads Experiments and Conversion Lift studies: if you are relying on user-based cookie splits rather than matched-market geo holdouts, your incremental ROAS is likely overstated by 25% to 40%.
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