Google Ads

How Performance Max Quietly Took Over Your Google Ads Budget — And What To Do About It

Joey Sew · April 2026 · 7 min read

Your Google Ads account is probably running a mix of Search and Performance Max campaigns. If you have been running both for more than a year, there is a reasonable chance PMax is consuming a significantly larger share of your budget than it did twelve months ago — and you did not decide that.

This is not a configuration error. It is how Performance Max is designed to behave. Understanding the mechanism, the impact, and what you can actually do about it is increasingly important for any ecommerce brand spending meaningfully on Google.

What Performance Max actually is — and what it optimises for

Performance Max is Google's fully automated campaign type. It serves ads across Search, Shopping, YouTube, Display, Gmail, Maps, and Discover from a single campaign, using machine learning to allocate budget across all surfaces.

The promise: Google's AI finds conversions wherever they exist across every Google channel, more efficiently than a human managing separate campaigns.

The reality: the algorithm optimises toward the path of least resistance — and the path of least resistance is almost always warm traffic. Best-selling products, retargeting audiences, and branded searches all convert at high rates. PMax pursues them aggressively because they look like performance to the algorithm, even though they represent revenue that was largely going to arrive anyway.

Kirk Williams, one of the most cited ecommerce Google Ads specialists, put it plainly: "PMax works too well at finding warm traffic. The hard work of incremental marketing isn't always pretty and doesn't always scale well."

The budget migration nobody planned

Performance Max and Search campaigns can both show ads for the same search queries. When this happens, Google's documentation says Search should win the auction. In practice, the interaction is more complicated.

An Adalysis study covering 3,300 campaigns found that when PMax and Search were both eligible for the same search terms, Search typically delivered higher conversion rates. Despite this, PMax frequently captured the traffic — absorbing queries that dedicated Search campaigns with tighter keyword control would have handled more efficiently.

The result, over months, is a systematic drift. Search impression share declines. Budget flows to PMax. The Search campaign appears to underperform. Budget gets reduced further. PMax grows to fill the gap.

In one ecommerce account we tracked over two years:

• January 2023: 80% Search, 20% PMax
• January 2025: 19% Search, 79% PMax

Nobody made a budget decision. The algorithm made it.

This is consistent with industry-wide data. Analysis of 4,000+ PMax campaigns found that PMax cost share across ecommerce accounts peaked at 82% in May 2024. It has since declined by nearly 6% as advertisers deliberately return budget to Search and Standard Shopping — but the default trajectory without active management still runs toward PMax dominance.

Kirk Williams was direct after reviewing his client portfolio in early 2025: "Has PMax jumped the shark? IMO, it has. We've never seen PMax perform consistently worse than it has moving into 2025, with little to no strategy shifts on our end. We have begun transitioning to Search and Standard Shopping more purposefully with obvious revenue and efficiency increase."

The transparency problem — what changed in 2025 and what didn't

For the first three years of Performance Max, the campaign type was genuinely opaque. No search term reports. No channel-level spend breakdowns. No campaign-level negative keywords. Advertisers were making significant budget decisions with almost no visibility into where the money was going.

Google addressed much of this at Google Marketing Live 2025. Three significant updates:

• Full search term reports for PMax are now available alongside Search campaign data in the standard search terms interface
• Campaign-level negative keywords — up to 10,000 per campaign — can be added directly in the Google Ads interface without contacting support
• Channel performance reporting shows how PMax budget splits across Search, Shopping, YouTube, Display, Gmail, and Maps

These are genuine improvements in a campaign type that was long overdue for more transparency. But Jyll Saskin Gales, a Google Ads coach and former Googler, captured the critical limitation: "There is not a control piece to go along with this, and Google has no plans to provide one."

You can now see that PMax is allocating 60% of its budget to YouTube and Display. You cannot instruct it to stop. You can see which search terms are triggering your PMax ads. You can add negative keywords to block the worst ones. But how much of your total spend goes to Search versus every other surface remains entirely within Google's control.

Transparency without control is better than a black box. It is not the same as control.

How to detect spend mix drift in your account

Step 1: Pull campaign-level spend data for the last 24 months.

Export from Google Ads at the campaign level with the campaign type column included. Use whatever history is available if 24 months is not.

Step 2:Calculate each campaign type's share of total Google spend per month.

Build a simple table: month, Search %, PMax %, Shopping %, other %. A spreadsheet is sufficient.

Step 3: Look for a trend.

If Search percentage has been declining while PMax has grown without a deliberate budget decision, you have spend mix drift.

Step 4: Use Shopify as your performance denominator.

In months where Search held a higher share, what was your blended MER — Shopify Online Store net sales divided by total ad spend? In PMax-dominant months, what was it? If MER was stronger when Search had more budget, the drift is costing you in real business terms. Platform-reported ROAS will not show this because PMax is effective at claiming credit for revenue that was going to arrive regardless.

What to do about it

Do not simply pause PMax. PMax is effective for Shopping — particularly for accounts with large product catalogues where managing every SKU in separate campaigns is impractical. Research shows accounts running PMax and Search together with clearly defined roles outperform either campaign type alone. The goal is structured coexistence, not elimination.

Add strong audience signals to PMax. Without audience signals, PMax defaults to whatever converts most easily — warm audiences and brand traffic. Upload your customer purchase list and high-value customer segment. This pushes the algorithm toward finding genuinely new customers rather than reclaiming traffic that was already yours.

Protect your brand in a dedicated Search campaign. Your highest-converting searches — people typing your brand name — should be captured in a Brand Search campaign where you set the bids, control the ad copy, and see every query. Do not let PMax absorb this traffic unmonitored.

Use the PMax search term report actively. Now that search term data is available for PMax, apply the same intent cluster analysis you use for Search. If visible PMax terms skew toward informational or stockist intent, add negative keywords at the campaign level. This is now straightforward in the Google Ads interface.

Monitor Search impression share weekly. A declining impression share in your best-performing Search campaigns, without a corresponding budget reduction, is a leading indicator that PMax is encroaching on your best traffic. Catch it early.

Set explicit budget floors for Search. Review campaign budgets monthly. If your highest-converting Search campaigns are running below their impression share targets due to budget constraints while PMax runs uncapped, correct this manually.

The visibility principle

Performance Max is not inherently bad. The transparency improvements in 2025 — search term reports, channel-level breakdowns, campaign-level negative keywords — represent genuine progress after years of advertiser frustration.

The problem is default behaviour. The algorithm, left unguided, optimises toward the traffic that converts most easily — which is almost always the traffic you were already capturing through branded search and warm retargeting audiences. Over time this produces an account that looks productive on Google's internal metrics while your actual Shopify revenue, measured against total spend, stagnates.

Independent measurement — blended MER anchored to Shopify — is the only way to honestly evaluate whether your PMax campaigns are generating genuinely incremental revenue or efficiently reclaiming what was already yours.