How Performance Max Cannibalises Your Brand Traffic (and What to Do)

Performance Max is Google's most powerful campaign type — and its most opaque. It uses machine learning to serve ads across Search, Display, YouTube, Gmail, Maps, and Discover, optimising for whatever conversion goal you set.

The problem is that PMax has a dirty secret. It loves brand traffic. And unless you take explicit steps to prevent it, PMax will quietly consume your brand search volume, claim credit for conversions that were already yours, and inflate its reported performance while adding little or no incremental value.

This is not a minor issue. For many advertisers, PMax brand cannibalisation represents thousands of pounds per month in misattributed spend. Understanding how it works — and how to stop it — is essential for anyone running Performance Max alongside brand campaigns.

How Performance Max works (the relevant parts)

PMax is designed to maximise conversions within a given budget. Google's algorithm decides where to show your ads, what creative to use, and who to target. You provide the assets (text, images, video, URLs), set a budget and conversion goal, and the algorithm does the rest.

The algorithm's objective is simple: find the cheapest conversions possible. And this is where the problem starts.

The path of least resistance

When PMax is looking for conversions, it evaluates all available signals to find users who are most likely to convert. Users who are already searching for your brand name are, by definition, the most likely to convert. They know who you are. They want your product. They are ready to buy.

From the algorithm's perspective, serving an ad to someone searching "YourBrand pricing" is a guaranteed conversion at minimal cost. Serving an ad to someone searching "best software for project management" is a gamble — they might convert, or they might not.

Given the choice, the algorithm will always prefer the sure thing. Brand traffic is the path of least resistance, and PMax walks it aggressively.

The attribution grab

When PMax serves an ad to someone searching for your brand and that person converts, PMax claims the conversion. This happens even if you have a separate brand campaign running. PMax takes priority in the auction for certain placements, and its multi-channel nature means it can intercept brand traffic across Search, Shopping, and other surfaces.

The result is that your PMax campaign shows brilliant performance metrics — low CPA, high ROAS, strong conversion volume — while your dedicated brand campaign (and your organic channel) show declining numbers. The total conversions have not increased. They have just been reshuffled to make PMax look like the hero.

How to detect PMax brand cannibalisation

The challenge with PMax is transparency. Google provides far less reporting data for PMax than for standard campaigns. But there are ways to detect the problem.

Check the Insights tab

In your PMax campaign, go to the Insights tab. Look at the "Search categories" and "Search terms" sections. If you see your brand name appearing as a top search category or among the top search terms, PMax is consuming brand traffic.

Google has improved PMax reporting over the past year, but the data is still aggregated and incomplete compared to standard search campaigns. You may see categories like "Brand searches" or your actual brand name listed among the top converting searches.

Compare before and after PMax launch

If you can access historical data from before your PMax campaign launched, compare:

Brand campaign impressions and clicks (before vs after PMax)
Brand campaign conversions (before vs after PMax)
Organic brand traffic in Google Analytics (before vs after PMax)

If your brand campaign metrics dropped when PMax launched — while PMax showed strong early performance — cannibalisation is the likely explanation.

Run a search terms analysis

While PMax does not provide a full search terms report, you can use scripts and third-party tools to extract more detail. Look specifically for:

Your brand name in PMax search queries
Brand + product terms appearing in PMax data
Navigation queries (e.g., "YourBrand login") in PMax

If more than 20% of your PMax conversion-driving queries contain your brand name, the campaign's real performance is significantly weaker than reported.

Monitor your brand campaign metrics

If PMax is cannibalising brand traffic, your dedicated brand campaign will show symptoms:

Declining impression share (PMax is winning auctions that your brand campaign used to win)
Fewer conversions attributed to the brand campaign
Lower click volume despite stable or growing brand search volume

Check your brand campaign's Auction Insights report too. If your own PMax campaign is not visible there directly, the symptoms above are your evidence.

Watch your organic brand metrics

In Google Search Console and Google Analytics, track:

Organic clicks for brand queries (trend over time)
Organic CTR for brand queries (should be stable or increasing)
Overall brand search volume (from Google Trends or Search Console)

If brand search volume is stable but organic clicks are declining, something is intercepting that traffic. PMax is a likely culprit.

The impact on your reported ROAS

Brand cannibalisation does not just waste money — it distorts your entire campaign measurement framework.

PMax looks better than it is

When PMax claims brand conversions, its reported ROAS and CPA include these easy wins. A PMax campaign that reports a 10:1 ROAS might actually be achieving 4:1 on genuinely incremental (non-brand) traffic. The brand conversions inflate the numbers, masking the campaign's true acquisition performance.

Non-brand performance is hidden

Because PMax blends brand and non-brand performance into a single number, you cannot see how well the campaign performs at its core job: finding new customers who did not already know about you. This opacity makes it very difficult to assess whether PMax is actually growing your business or just recycling existing demand.

Budget allocation becomes irrational

If PMax reports a 10:1 ROAS while your standard search campaigns report 4:1, the logical decision appears to be shifting more budget to PMax. But if PMax's inflated ROAS is driven by brand cannibalisation, you are actually shifting budget away from genuine acquisition campaigns toward a campaign that is largely claiming credit for existing customers.

This misallocation compounds over time, gradually hollowing out your real customer acquisition efforts while PMax absorbs more budget and claims more credit.

How to fix it: brand exclusions for PMax

Google introduced brand exclusions for Performance Max campaigns in 2023, after years of advertiser pressure. This feature allows you to prevent PMax from showing ads on searches containing your brand name.

How to set up brand exclusions

In Google Ads, navigate to your Performance Max campaign
Click on Settings
Scroll to "Brand exclusions" (under "Additional settings" or "Campaign settings" depending on your interface version)
Click "Edit brand exclusions"
Search for your brand name in the brand list
Select your brand and any variations
Save

If your brand does not appear in Google's brand list, you can request it be added. You can also add specific brand terms manually in some configurations.

What brand exclusions actually do

When you add a brand exclusion, PMax will not serve Search ads on queries that contain your brand name. This means:

"YourBrand" searches will not trigger PMax ads
"YourBrand pricing" will not trigger PMax ads
"YourBrand reviews" will not trigger PMax ads

However, brand exclusions have limitations:

They only apply to Search and Shopping placements. PMax can still target brand-interested audiences on Display, YouTube, and Discover.
They rely on Google's brand matching, which may not catch all variations, misspellings, or abbreviations.
They do not prevent PMax from targeting people who recently searched for your brand on other channels (audience-based targeting vs query-based targeting).

Despite these limitations, brand exclusions are essential. They address the most significant source of cannibalisation (Search) and should be activated in every PMax campaign.

After enabling brand exclusions

Once you enable brand exclusions, expect the following changes:

PMax metrics will decline. Reported ROAS will drop and CPA will increase. This is not because PMax has gotten worse — it is because the inflated brand metrics have been removed, revealing the campaign's true acquisition performance.

Brand campaign metrics will recover. Your dedicated brand campaign should see increasing impressions, clicks, and conversions as it reclaims the brand traffic PMax was taking.

Organic brand metrics may increase. Some brand searches that PMax was capturing may shift to organic, especially navigational queries.

Total conversions may stay roughly flat. This is the key test. If total conversions across all channels remain stable after enabling brand exclusions, PMax was not generating incremental value from brand traffic — it was just claiming credit.

Monitor all channels for 2-4 weeks after making the change. Use this period to establish the true, brand-excluded performance of your PMax campaign.

Beyond brand exclusions: additional steps

Maintain a separate brand campaign

If you are running PMax, you should almost certainly also run a dedicated brand search campaign. This gives you:

Direct control over brand ad copy and landing pages
Full search terms reporting for brand queries
The ability to set precise bids for brand terms
Clear attribution of brand traffic

Follow our brand campaign best practices to run this efficiently.

Review PMax asset groups

Check your PMax asset groups for brand-heavy content. If your asset groups include landing page URLs that are primarily brand pages (homepage, about us, pricing), PMax will naturally gravitate toward brand traffic even with exclusions in place.

Consider creating asset groups focused on specific products or acquisition themes, with URLs pointing to category or product pages rather than your homepage.

Audit your conversion tracking

PMax optimises for the conversions you tell it to optimise for. If your conversion setup includes low-value brand actions (like branded newsletter signups or support logins), PMax will chase these easy wins.

Ensure your PMax conversion actions reflect genuine business value — purchases, qualified leads, or significant engagement actions. Remove or deprioritise conversion actions that are disproportionately triggered by brand traffic.

Run periodic checks

Brand cannibalisation is not a one-time fix. PMax's algorithm evolves, and new campaign changes can reintroduce the problem. Schedule monthly reviews of:

PMax search categories and terms (looking for brand queries)
Brand campaign impression share and volume trends
Organic brand traffic trends
Total conversion volume across all channels

The bigger picture: PMax and brand strategy

Performance Max is a powerful tool for reaching new audiences across Google's network. But its power comes with opacity, and its optimisation algorithm does not distinguish between incremental and non-incremental conversions. It simply finds the cheapest conversions available, and brand traffic will always be the cheapest.

Advertiser awareness of this problem has grown significantly, and Google's introduction of brand exclusions was a direct response to the pressure. But the default setting is still no exclusions — meaning every new PMax campaign starts by cannibalising brand traffic until the advertiser actively prevents it.

If you are running PMax and have not enabled brand exclusions, do it today. Then monitor the impact, adjust your expectations for PMax performance, and assess whether the campaign's true (non-brand) performance justifies its budget.

For help understanding your brand traffic exposure across all campaigns — including PMax — try our free brand audit. We will show you where your brand clicks are going, how much you are spending on non-incremental brand traffic, and what you could save with proper campaign structure.

And if you want to quantify the financial impact of PMax cannibalisation, our brand spend calculator can model the difference between reported and actual incremental ROAS — giving you the data you need to make informed budget decisions.