Performance Max Campaigns: Search Themes, Budgets and Getting Control Back

Performance Max (PMax) is Google’s all-in-one campaign type. A single campaign can show your ads across Search, Shopping, YouTube, Display, Discover, Gmail and Maps, with Google’s automation deciding where, when and to whom.

That automation can work very well, but left to its own devices PMax can overspend, compete with your existing Search campaigns and leave you with little idea of what’s actually driving results. This guide covers how to guide it with search themes, how to set and scale budgets, and how to protect the rest of your account.

What’s Changed With Performance Max

PMax used to be criticised as a black box. Google has since added a lot more visibility and control, including:

• Negative keywords, at campaign level, plus shared negative keyword lists that can be applied across several PMax campaigns.
• Search terms reporting, so you can see which searches your ads appeared for.
• Channel performance reporting, showing how results split across Search, YouTube, Display and other placements.
• Device and age targeting controls.
• Full asset reporting, with conversions, cost and clicks for individual assets.
• More search themes, with the limit raised from 25 to 50 per asset group.

If you set PMax up a while ago and haven’t revisited it, these controls are worth reviewing first.

What Are Search Themes?

Search themes let you tell Google which searches are relevant to your business, so PMax can find the right people more quickly. Think of them as giving the automation context rather than strict instructions. They replaced the old custom segments based on search activity, which Google converted automatically.

How search themes interact with your Search campaigns

Running PMax alongside standard Search campaigns can mean the two compete for the same searches. Google uses an order of priority to decide which campaign shows:

• Exact match keywords in your Search campaigns take priority over everything else, including search themes.
• Search themes have the same priority as broad and phrase match keywords.
• When there’s a tie, Ad Rank decides.

So if your Search campaigns rely only on broad and phrase match, PMax can end up taking traffic you’d rather they kept. Using exact match for your most important keywords keeps that traffic in your Search campaigns, where you have more control.

Tips for using search themes well

• Fill the gaps your website leaves. If your landing pages are light on content, search themes help Google understand what you offer.
• Be clear about what you sell. Search themes should describe your products or services plainly, even if your ad copy is more creative.
• Quality over quantity. You can now add up to 50 per asset group, but a focused set of relevant themes works better than filling every slot.
• Consider competitor terms, particularly if you’re a newer brand that people don’t yet search for by name.
• Test the impact. Running a test with and without search themes is the clearest way to see what difference they make.

How to Allocate Your PMax Budget

Most businesses approach PMax budgets in one of two ways. Either they starve it with a minimal budget and wonder why conversion volume is weak, or they put too much into it and watch their Search and Shopping results suffer. A simple framework avoids both.

Start with a split across campaign types

As a starting point, we often use a 70-20-10 split:

• 70% to Performance Max
• 20% to branded Search, to protect your highest-intent traffic
• 10% to experimental or specialist campaigns

Adjust that to suit your business. Ecommerce accounts with good product feeds often suit a heavier PMax share. Lead generation and B2B accounts, where lead quality matters more than volume, usually suit a lighter one, with more budget kept in Search where you control the keywords.

Whatever the split, each campaign needs enough budget to generate around 30 conversions a month, or the automation won’t have enough data to optimise properly.

Split PMax by performance tier

For ecommerce, grouping products by performance stops your best sellers competing with everything else for the same budget:

• Tier 1 (around 60% of PMax budget): your best performers, with higher return on ad spend (ROAS) targets.
• Tier 2 (around 30%): solid performers worth testing and growing.
• Tier 3 (no more than 10%): new products or underperformers, with spend capped.

For example, if leather jackets return 6:1 and denim returns 2.5:1, leather jackets should get the bigger share.

Factor in your margins

ROAS doesn’t account for profit. A 5:1 ROAS on a product with a 15% margin can make you less money than a 3:1 ROAS on a product with a 40% margin. Higher-margin products can afford lower ROAS targets, while low-margin products need higher ones to stay profitable.

Start with Maximise Conversions

New PMax campaigns should usually start on Maximise Conversions (or Maximise Conversion Value) until they’ve built up 30 to 50 conversions. Then move to Target CPA or Target ROAS. Setting aggressive targets too early slows delivery and drags out the learning period.

Scale gradually

Change budgets in steps of 15% to 20%, and wait 7 to 14 days before judging the result. Frequent or large changes push the campaign back into its learning phase. The same applies when reducing budgets.

Protecting the Rest of Your Account

Moving too much budget from Search into PMax is one of the most common mistakes we see. It often leads to lost visibility on branded searches, rising costs and a drop in overall account ROAS.

• Keep a dedicated branded Search campaign. It protects your highest-intent, cheapest traffic.
• Use brand exclusions in PMax if you don’t want it taking credit for searches that would have converted through your brand campaign anyway.
• Add negative keywords to block irrelevant or low-quality searches.
• Only scale PMax when the whole account is healthy. If PMax is performing and your other campaigns are holding up too, you can move its share up towards 75% to 80%. Don’t scale it at the expense of everything else.

Measuring Performance Max

Judge PMax on the whole account, not just the campaign:

• Campaign level: conversions per month, cost per acquisition, ROAS against its target and impression share.
• Account level: total conversions, blended ROAS across all campaigns and whether your branded Search results are holding up.
• Search terms and channel reports: check where your budget is actually going.

Give any significant change four to six weeks of data before deciding whether it worked.

Common PMax Mistakes

• Setting ROAS targets with no historical data to base them on
• Treating PMax as a black box and never checking its reports
• Underfunding it, so it never has enough data to learn
• Letting it cannibalise branded and high-intent Search traffic
• Making decisions based on a single week of data

Your PMax Checklist

1. Agree your split between PMax, branded Search and testing, based on your business model.
2. Group products into performance tiers, and factor in margins.
3. Add search themes, negative keywords and brand exclusions.
4. Start on Maximise Conversions, then move to Target CPA or ROAS.
5. Scale budgets in 15% to 20% steps, with 7 to 14 days between changes.
6. Review search terms, channel reports and blended account results monthly.
7. Make structural changes quarterly, not weekly.

Getting More From Performance Max

PMax works best when it’s given clear direction, good data and a sensible budget, and kept from crowding out the campaigns you already rely on. If you’d like a second opinion on how your account is set up, our free Google Ads audit will show you where PMax is helping, where it’s costing you and what to change first.