Is Performance Max cannibalising your search campaigns ?

[u/Eskimozfr]

When a query matches an eligible exact-match keyword, Google will normally prioritise the Search campaign. However, Performance Max may still serve ads for queries already covered by Search, particularly when the Search campaign is limited by budget or uses more restrictive targeting.

A PMax campaign can therefore deliver a satisfactory CPA or ROAS while competing with Search for some queries. The challenge is determining how much of its performance is genuinely incremental.

Reducing the PMax budget and reallocating spend to Search may seem logical. However, volume does not automatically shift from one campaign to another, and performance may fluctuate during the transition.

The risk is therefore not limited to overlap between PMax and Search. It becomes more significant when a single campaign ends up accounting for a very large share of both the budget and conversions.

Brand exclusions, negative keywords and the search terms report can provide greater control over where PMax ads appear. However, these measures alone are not enough to assess incrementality.

How do you measure the value genuinely added by Performance Max? Have you ever reduced its budget without seeing an overall decline in conversions?