Performance Max search themes: a practical guide

Performance Max gives Google's AI a lot of room to decide where your ads show. Search themes are the lever you pull when you want to nudge that decision. This guide explains what they are, where they fit alongside AI Max for Search, and how to build a theme list that actually improves reach without burning budget on irrelevant queries.

What search themes are

Search themes are an optional input in Performance Max. Per Google's docs, they let you indicate queries that you know your customers are looking for. Themes are additive: PMax already matches you to queries using your URLs, assets, and feeds. Themes fill gaps where your landing pages and product feeds use different terminology than what people actually type into Google.

Themes work across all PMax inventory: Search, YouTube, Gmail, Discover, Maps, and Display. On Search specifically, themes share priority with phrase and broad match keywords in your Search campaigns. Exact match keywords that are identical to the query still win over themes.

A few hard limits and rules to know:

You can add up to 25 search themes per asset group.
Themes respect brand exclusions at the PMax level and account-level negative keywords.
Themes are optional. Skip them entirely and PMax still serves, just on signals from your assets and feeds alone.

Custom segments based on past search activity were automatically upgraded to search themes in early 2024. You can no longer add or edit those segments in PMax. Custom segments based on interests still exist, but themes are now the right input for query intent steering.

How search themes relate to AI Max

This is where accounts get confused. AI Max for Search and PMax search themes are different features for different campaign types. AI Max is a Search campaign optimisation layer that includes search term matching, text customisation, and final URL expansion. Themes are a PMax-only input.

The overlap is functional, not structural. Both nudge Google's AI toward relevant query intent. AI Max does it from inside a Search campaign using broad match plus your assets and landing pages. Themes do it from inside a PMax campaign as a list of explicit hints.

If you run a Search campaign with AI Max enabled, you don't need search themes for that campaign. Themes only matter in PMax. AI Max became generally available in April 2026 after beta in May 2025. PMax themes have been available since late 2023 and were upgraded from custom segments in early 2024.

Sourcing theme candidates

The search terms report inside PMax is the best starting point. Google Ads > Campaigns > your PMax campaign > Insights and reports > Search terms. Look for queries that PMax matched but you didn't explicitly target. The themes you should add are the ones that look like real customer intent but aren't covered by your assets or feeds.

Other sources worth pulling from:

Your Search campaign search terms reports. If a Search campaign query converts well, it probably converts well as a PMax theme too. Cross-reference and add the high-intent ones.
Google Keyword Planner. Filter by your product category and look at the "discover new keywords" view. Themes don't need to be exact match, so phrase-style hints work well here.
Competitor pages. Read how competitors describe the same products. Different terminology is a strong theme candidate.
Customer reviews and forums. The language real customers use is often very different from your product feed terminology. That gap is where themes earn their keep.
Sales team input. The words your sales team hears in calls are the words your customers type in searches. Capture them.

Aim for themes that hint at intent the feed doesn't already cover. If your feed already lists "red running shoes", a theme of red running shoes adds nothing. A theme of marathon trainers or jogging shoes for flat feet is what fills the gap.

Categorising themes by intent

Five buckets cover most theme candidates. Pick themes from one or two buckets per asset group so the AI gets a coherent signal rather than a mixed bag.

Research intent. how to choose running shoes, what to look for in trainers. People comparing options.
Consider intent. best running shoes for flat feet, top marathon trainers 2026. People narrowing the field.
Buy intent. buy running shoes online, running shoes free delivery, running shoe discount code. People ready to purchase.
Use case intent. running shoes for treadmill, trail running shoes waterproof. People with a specific scenario in mind.
Audience intent. running shoes for beginners, running shoes for wide feet. People self-identifying a need.

Pick themes that genuinely fit the asset group's offer. Don't add running shoes themes to an asset group for hiking boots. The AI will mix signals and performance will degrade.

Using our Keyword Combiner

Bulk-generating theme candidates? Our Keyword Combiner builds long lists from word groups. Feed it intent modifiers and product terms, and it cross-combines them into hundreds of candidate phrases in seconds.

Typical workflow: list your five intent buckets as separate word groups, add your product terms as a final group, then run the combiner. Skim the output for relevance, drop it into the PPC Keyword Cleaner to dedupe and trim, then copy the keepers into PMax. Most accounts end up picking 15-20 strong themes out of 200+ candidates.

Common mistakes

Adding themes that duplicate your feed. If your feed says "red running shoes", a theme of red running shoes adds nothing. Look for the gap, not the overlap.
Mixing intents in one asset group. An asset group with both research-intent and buy-intent themes confuses the AI. Split them into separate asset groups.
Skipping account-level negative keywords. Themes respect account-level negatives. If you haven't built a negative list, your themes can still drive irrelevant spend.
Treating themes as keywords. Themes are hints, not targeting. PMax still serves beyond what you list. Don't expect theme-only precision.
Setting and forgetting. Use the search terms source column (added in 2024) to see which conversions came from explicit themes vs keywordless matching. Adjust based on what actually works.
Hitting the 25-theme limit with weak candidates. Better to add 8 strong themes than 25 mediocre ones. Quality over count.

FAQ

How many search themes should I add per asset group?

Up to 25 is the Google cap. In practice, 8-15 strong themes per asset group outperforms 25 mediocre ones. Start with the obvious gaps in your feed, layer in intent modifiers, and stop when the candidates start feeling like duplicates.

Do search themes work without AI Max?

Yes. AI Max is a Search campaign feature. Themes are a PMax feature. They run on separate campaigns and don't interact.

What's the difference between search themes and audience signals?

Themes steer which search queries PMax targets. Audience signals steer who PMax targets based on demographics, behaviour, and interests. They're complementary inputs to different parts of the matching system.

Can I bulk-upload themes?

Yes, via Google Ads Editor. Themes use the same CSV import flow as other PMax inputs. Format them as a single column with one theme per row, then map to the search themes field during import.

Keyword Combiner. The tool described in section 5. Cross-combines intent modifiers with product terms to bulk-generate theme candidates.
PPC Keyword Cleaner. Dedupe, sort, and trim a candidate list before pasting into PMax.
Broad vs Phrase vs Exact match guide. Background on positive match types since themes share priority with phrase and broad match keywords.