Quick answer: Performance Max campaigns will cannibalize your branded search traffic by default. The most reliable fix is adding your brand terms as negative keywords at the account level, not just the campaign level, ensuring your dedicated branded Search campaign has an uncapped budget, and switching that campaign's bid strategy to Target Impression Share so it always outcompetes PMax in the auction.
What Brand Cannibalization Actually Looks Like
You run a clean branded Search campaign. It converts at 8x ROAS. You've had it isolated and performing well for months. Then you launch a Performance Max campaign.
Two weeks later, your branded campaign's impression share has dropped 40%. Your PMax numbers look great. Your total account ROAS looks about the same, maybe a little better. But you didn't add any new customers. PMax just quietly walked into the room and claimed credit for the traffic your brand already owned.
This is what practitioners mean when they say it is basically paying yourself for clicks. PMax didn't go find new buyers. It intercepted people who were already searching for you by name, served them an ad for something they were going to click anyway, and reported a conversion.
The branded Search campaign your team worked to optimize isn't broken. It's being outcompeted in the auction by a campaign that Google has given priority to by default.
Why PMax Gets Priority Over Your Branded Campaign
Google's auction rules do favor Performance Max over Search in certain conditions. The general principle is that exact match keywords in a Search campaign take priority over PMax, but only when your Search campaign wins on Ad Rank.
There are two conditions where that priority breaks down:
Your branded campaign runs out of budget. The moment your branded Search campaign hits its daily cap, PMax moves in and captures every branded impression that campaign would have won.
If your branded Search campaign is ever Limited by Budget, the second it throttles pacing for the day, PMax takes over.
Your Search campaign loses the Ad Rank auction. If your branded campaign isn't bidding aggressively enough to maintain top position, PMax can win the impression. This typically happens when campaigns are running manual CPC or a conservative automated strategy that isn't keeping pace.
The Fixes That Actually Work
1. Add brand terms as negative keywords at the account level
Campaign-level brand exclusions in PMax settings help, but they are not fully reliable, especially for close variant matching. The only consistently effective control is adding your brand terms to a negative keyword list applied at the account level.
Add your brand terms as negative keywords at the account level, not just the campaign level. That is the only reliable way to keep PMax out of branded traffic.
This includes your brand name, common misspellings, tagline variations, and any product names that are unique to your business.
2. Give your branded Search campaign an uncapped budget
If brand impressions matter to you, and they should, your branded campaign should never be limited by budget. Brand clicks are typically the cheapest in your account. The budget required to capture 100% of impression share for branded searches is usually a small fraction of your total spend.
It will cost you only about 1-5% of your total budget.
An uncapped brand budget removes the primary opening PMax uses to take over.
3. Switch to Target Impression Share bidding on your branded campaign
If your branded Search campaign is on manual CPC or Maximize Conversions, consider switching it to Target Impression Share targeting 90-100% of the absolute top of page. This strategy bids aggressively enough to maintain Ad Rank regardless of what PMax is doing.
This forces the system to bid aggressively enough to maintain the Ad Rank, blocking PMax from sneaking in.
4. Build out exact match coverage for every brand variation
Phrase and broad match keywords in your branded campaign do not get the same auction priority as exact match.
An Exact Match keyword in a Search campaign will take priority over PMax. However, this only applies if your Search campaign wins better at that exact auction.
Map out every realistic variation of how someone searches for your brand: full name, short name, common misspellings, product-specific terms. Each should be an exact match keyword in your branded campaign.
The Monitoring Problem
Even with all of these controls in place, this isn't a set-it-and-forget-it fix. PMax brand exclusions are applied inconsistently for close variants. Google updates how auction priority works without broadcasting it. An account-level negative keyword list added today may not catch every variation of your brand term that shows up next quarter.
Practitioners who've dealt with this for years describe it as a cat-and-mouse game. The only realistic approach is monthly monitoring: check your branded campaign's impression share, compare it against the same period the prior month, and check the PMax insights tab for any branded search term activity.
If branded impression share is dropping without an obvious cause, PMax cannibalization is the first thing to investigate.
Should You Just Exclude Brand from PMax Entirely?
This depends on your goals and account structure. There's a legitimate argument for including brand in PMax: branded traffic seeds the algorithm with high-quality conversion signals that improve PMax's performance on non-branded queries.
Without brand, you're basically asking Google to cold-start without your warmest signal.
A practical middle ground: run a small dedicated brand campaign alongside PMax rather than relying on PMax to capture branded traffic. The brand campaign controls your message and captures branded intent cleanly. PMax draws on the account-level signal from that brand traffic to improve its targeting, without being the one responsible for capturing it.
The structure looks like this: Brand Search campaign using Target Impression Share and an uncapped budget, plus PMax with brand excluded via account-level negatives.
FAQs
My PMax ROAS looks great. Does that mean it's not cannibalizing brand?
Not necessarily. PMax attribution includes all conversion paths, including view-through conversions from users who saw an ad and later searched for your brand directly. A high reported ROAS in PMax does not confirm that PMax is generating incremental conversions. Check your branded Search campaign's impression share before treating PMax numbers as evidence of real growth.
Will adding brand as a negative keyword at the account level hurt my PMax performance?
It can reduce PMax conversion volume and reported ROAS in the short term, because PMax can no longer claim credit for branded conversions. Whether your actual customer acquisition is affected depends on whether those branded conversions were incremental. To find out, run a brand exclusion test or a geo-split test and compare total revenue against a control period.
Can I use URL expansion settings to keep PMax off my brand pages?
URL expansion controls which landing pages PMax sends traffic to. It doesn't control which search queries trigger your ads. Turning off URL expansion is useful for controlling landing page behavior, but it won't stop PMax from showing for branded search terms.
My brand search campaign is losing impression share but PMax isn't showing for branded terms in the insights tab. What's happening?
PMax insights data is aggregated and incomplete. The absence of branded terms in the insights tab doesn't mean PMax isn't capturing branded traffic. It often just means the volume didn't clear the reporting threshold. Cross-reference impression share data from the Auction Insights report on your branded campaign instead.