It's the most debated topic in Google Ads right now: is Performance Max actually driving incremental results, or is it simply stealing conversions from your existing Search campaigns and taking the credit? After analyzing hundreds of accounts, here's what the data actually shows.
The Cannibalization Problem Explained
Here's what happens in many accounts: an advertiser launches PMax alongside existing Search campaigns. PMax starts reporting conversions and a strong ROAS. But total account conversions don't increase proportionally. Where are PMax's "new" conversions coming from? Often, they're coming from brand searches, remarketing audiences, and high-intent queries that Search campaigns were already capturing.
This isn't inherently wrong — Google designed PMax to compete in the same auctions as your other campaigns. When PMax has a higher Ad Rank for a given query, it wins the auction instead of your Search campaign. The problem is when advertisers see PMax's "great numbers" and increase its budget while cutting Search — only to find total performance stays flat or declines.
What the Data Actually Shows
Across our managed accounts, we've found that PMax cannibalization ranges from minimal (10-15% overlap) in well-structured accounts to severe (40-60% overlap) in poorly structured ones. The difference comes down to three factors: brand exclusions, campaign structure, and audience signal quality.
In accounts where we've implemented proper brand exclusions and tightly themed asset groups, PMax consistently delivers 25-40% incremental conversions — meaning these are conversions the account would not have gotten from Search alone. These come from Discovery, YouTube, Gmail, and Display placements where Search campaigns don't compete.
How to Prevent Cannibalization
1. Use Brand Exclusions
This is non-negotiable. Without brand exclusions, PMax will happily serve your ads on branded search queries — queries that your Search campaigns were already winning at a low CPA. Brand exclusions force PMax to find genuinely new traffic, which is where its multi-channel reach adds real value.
2. Run a Controlled Incrementality Test
The gold standard for measuring PMax's true impact is a hold-out test. Pause PMax for 2-4 weeks and compare total account performance (not just Search performance) to the period when PMax was running. If total conversions drop, PMax was driving incremental value. If they stay flat, PMax was cannibalizing.
3. Monitor Channel Distribution
If PMax is spending 70%+ on Search, it's likely cannibalizing your Search campaigns. Healthy PMax campaigns should distribute budget across Search (30-40%), Display (20-30%), YouTube (15-25%), and Discover/Gmail (10-20%). If it's all going to Search, your audience signals and asset groups need work.
Our Recommended Account Structure
- • Branded Search Campaign: Exact and phrase match brand terms. Full control, always-on.
- • Non-Branded Search Campaign: High-intent keywords with manual or tCPA bidding.
- • PMax (with brand exclusions): Expands reach across YouTube, Display, Discover, and long-tail Search queries.
- • Remarketing: Dedicated remarketing for high-value audiences (consider excluding from PMax to avoid overlap).
This structure ensures each campaign type has a clear role. Search handles high-intent queries with full transparency. PMax drives incremental reach across channels. Remarketing re-engages warm audiences with tailored messaging. No overlap, no cannibalization.
Worried about PMax cannibalization in your account? Get a free audit and we'll run an incrementality analysis.