How to Stop Performance Max from Cannibalising Your Search Results
Performance Max campaigns are powerful because they can scale your advertising across Google’s entire inventory. But here’s what Google won’t tell you: if you don’t manage them properly, they’ll steal traffic from campaigns that were already working, and take all the credit.
The problem is simple – PMax doesn’t respect boundaries. It doesn’t care that you’re already ranking organically for a keyword. It doesn’t care that your Search campaign is converting profitably on brand terms. It just sees an opportunity to serve an ad and takes it.
This isn’t theoretical because we see it happen constantly. Brands launch P and with some impressive initial numbers, increase their spend and max our their budgets. A few months down the line, they realise that overall site revenue has stagnated, profitability has declined, and they can’t quite figure out what’s gone wrong.
What PMax Cannibalisation Looks Like
Cannibalisation happens when PMax competes with your existing traffic sources for the same users. Instead of finding new customers, it’s just moving existing ones around your account.
Here’s the technical bit: Google’s auction system prioritises campaigns based on multiple factors including bid, quality score, and campaign type. PMax campaigns often get preferential treatment in auctions, meaning they can outbid your Search campaigns for the same keywords, even when your Search campaigns were performing better.
Signs Your PMax is Stealing Traffic
- Your PMax campaign suddenly starts showing high volume on branded keywords. This is almost always cannibalisation since people searching your brand name were likely to convert anyway.
2. You’re seeing more conversions in PMax but your total revenue hasn’t grown proportionally. The conversions are probably coming from existing traffic sources.
3. Your organic search traffic decreases for keywords that PMax is now targeting. Google’s showing your ads instead of your organic results.
4. Your existing Search campaigns see reduced impressions or higher CPCs for keywords that overlap with PMax targeting.
How to Stop the PMax Cannibalisation
Exclude Brand Terms in PMax
This is non-negotiable. Add your brand name, product names, and branded variations as negative keywords in your PMax campaign.
The technical reason is simple; brand searches have high conversion rates and low costs when handled by dedicated Search campaigns. PMax will bid aggressively on these terms and inflate your costs.
Use Exact Match Negatives for Top Organic Keywords
Identify keywords where you rank in the top 3 organic positions. Add these as exact match negative keywords in PMax.
Why exact match? It prevents PMax from targeting the specific keyword while allowing it to target related variations that might not have organic coverage.
Example: If you rank #1 for “blue running trainers”, add [blue running trainers] as a negative keyword. PMax can still target “best blue running trainers” or “blue running trainers UK”.
Prioritise Exact Match Search Campaigns
Structure your Search campaigns with exact match keywords for your most important terms. Set these campaigns to higher priority and higher bids than your PMax campaigns.
The technical bit: Exact match keywords in Search campaigns will typically win auctions against PMax’s broad targeting when the search query exactly matches your keyword.
Limit PMAX Search Themes
In your PMax campaign settings, remove or limit Search themes that overlap with your existing Search campaigns. Focus PMax on discovery and finding new audiences rather than competing for known keywords.
Use Audience Signals Strategically
Configure your PMax audience signals to target users who are less likely to find you through Search or organic channels. Focus on demographic or interest-based targeting rather than keyword-based signals.
Test and Measure the Impact
The only way to know if cannibalisation is happening is to test. Consider the following approaches to testing:
Pause test: Pause your PMax campaign for 2-4 weeks and monitor what happens to your Search and organic performance. If they improve significantly, you were experiencing cannibalisation.
Brand exclusion test: Add brand terms as negatives in PMax and measure the impact on your overall branded conversion volume. If total branded conversions don’t drop, PMax was cannibalising.
Data test: Quite simply – if your spend on PMax campaign has pushed up your overall paid search spend, but your revenue has not improved – you might just be taking conversions from another channel and moving them into PMax.
The Bottom Line
PMAX isn’t a set-and-forget solution. It’s a powerful tool that needs constraints to work effectively. Without proper management, it becomes an expensive way to rebuy traffic you were already getting.
The goal isn’t to eliminate PMAX. It’s to make sure it’s finding genuinely new opportunities rather than competing with your existing success.
Start with brand exclusions. Add negative keywords for your top organic terms. Test the impact. Your overall performance will improve when each campaign type focuses on what it does best.
