Performance Max · Diagnostics
How to Fix Performance Max Cannibalisation
By Chris Avery, Founder · Updated 26 September 2026 · 5 min read
PMax can appear against brand queries and reach existing customers. The first job is to find out where it served; the next is to decide whether that spend added anything to the business.
Start with the account, not a percentage
Read the available PMax search terms and channel reporting alongside branded Search, Shopping, organic demand and first-party orders. Keep undisclosed queries unknown. A high brand share tells you what was attributed, not how many orders would have happened without advertising.
Choose the right controls
Google's PMax brand exclusions can restrict specified brand queries on eligible search inventory, with an option to allow Shopping for excluded brands. They are not an existing-customer exclusion. Review the actual settings in each campaign before assuming coverage.
For specific queries, Google also supports campaign-level PMax negative keywords on Search and Shopping inventory. Keep brand and non-brand decisions separate: excluding brand queries can change reported campaign results without showing whether total business sales changed.
Understand Search overlap
Google prioritises an eligible exact-match Search keyword identical to the query over PMax. Other matches depend on Google's prioritisation rules and eligibility; no fixed impression-share target guarantees control. Review actual search terms and campaign settings rather than assuming Search and PMax bid against each other and raise each other's prices.
Search themes are advertiser-provided signals, not a report of the terms on which ads appeared. Use search terms reporting for that check.
Test the commercial question
Agree the outcome first, ideally contribution after advertising across the business. If volume and geography permit, compare balanced test and control areas with a pre-agreed decision rule. Account for stock, promotions, price, other media and conversion lag. A pause, a changed brand share or a before-and-after chart alone cannot establish incrementality.
For the full signal, alternative explanation and next-check framework, read our PMax brand diagnostic. Our Performance Max management explains how these decisions fit ongoing account work.
Common questions
What is Performance Max cannibalisation?
It is the concern that PMax is receiving credit for demand another route might have captured. Overlap in reporting is a diagnostic signal, not proof of lost incremental sales.
How do I test whether PMax is capturing existing brand demand?
Inspect disclosed search terms and channel reporting, then agree a controlled test with comparable groups, a commercial outcome and checks for stock, promotions, price and other media. A simple before-and-after comparison cannot isolate lift.
Do PMax brand exclusions stop all existing-customer advertising?
No. Brand exclusions apply to specified search inventory; Shopping can be allowed for excluded brands. They do not exclude every existing customer or establish that remaining sales are incremental.
Does an exact-match Search keyword always take priority over PMax?
Google prioritises an eligible exact-match Search keyword identical to the search term over PMax. This does not mean every near match is covered or that a target impression-share threshold guarantees an outcome.
Can I use negative keywords in Performance Max?
Yes. Google supports campaign-level negative keywords for PMax Search and Shopping inventory. Brand exclusions are another control for brand-related queries; choose the setting that matches the intended coverage.
Can PMax displace organic traffic?
Paid and organic results can overlap, but a change in organic sessions alongside PMax spend does not identify the cause. Compare total commercial outcomes in a feasible controlled test before treating displacement as a budget finding.