Audience Targeting

Custom Segments vs In-Market Audiences: Build or Pick

In short: Both attach intent-flavored audiences to Display, Video, and Demand Gen ad groups, and both are built by Google from user behavior. The difference is authorship: with in-market you pick a finished category from Google's catalog, while with custom segments you hand Google keywords, URLs, or app names and it assembles an audience around your inputs. That makes custom segments the tool for niches the catalog misses, and in-market the tool for categories it covers well. If a catalog category genuinely matches what you sell, start there; build a custom segment when the taxonomy has no shelf for you.

By the AdFlint research team · Fact-checked against current Google and Meta platform behavior · Last reviewed July 2026

Custom Segments

Lets you define your own Google audience from keywords people search, websites they browse, or apps they use, instead of picking a prebuilt segment.

You supply search terms, URLs, or app IDs, and Google assembles an audience of people whose behavior matches those signals across Display, Video, and Demand Gen. It is the closest thing to keyword targeting outside Search, and it replaced the older custom affinity and custom intent segments. Most accounts overload one segment with unrelated inputs, which blurs the signal Google builds against.

Full definition

In-Market Audiences

Targets people Google has identified as actively researching or comparing products in a defined category, based on their recent search and browsing behavior.

You attach an in-market segment to a Display, Video, Demand Gen, or Search ad group and Google matches users whose recent activity signals active purchase research. Reach for it when you want intent-led reach beyond your own keyword footprint. The common mistake is applying it to Search as targeting rather than observation, which narrows an already intent-qualified audience for no gain.

Full definition

Side by side.

The differences that actually change what happens in your account.

 Custom SegmentsIn-Market Audiences
What you enterYour own search terms, website URLs, or app names as seed signals.Nothing - you select a finished category from Google's list.
Who defines the audienceYou seed it and Google interprets the seeds, so quality depends on your inputs.Google defines and maintains it end to end with no input from you.
Niche coverageCan approximate audiences the catalog has no category for, including competitor-adjacent ones.Limited to the categories Google has chosen to build and maintain.
Where it can runDisplay, Video, and Demand Gen only - it cannot be applied to Search.Display, Video, and Demand Gen, plus Search as an observation or targeting layer.
How keywords are readOn YouTube and Demand Gen, Google can match people who searched those terms on Google; on Display the same words degrade to interest-style matching.Not applicable - membership comes from Google's own category model, not your keywords.
Iteration loopUnderperformance is debuggable - edit, split, or retheme the inputs and remeasure.Your only levers are switching categories or layering exclusions on top.
Failure modeOne segment stuffed with unrelated keywords and URLs, blurring the signal Google builds against.A category one level too broad for your product, paying for shoppers who will never want your variant.

What actually separates them.

01

Custom segments never attach to Search campaigns, while in-market can ride along on Search as observation, so only one of them can inform your keyword bidding.

02

The same custom segment inputs produce different behavior by surface - search-term matching on YouTube and Demand Gen, interest-style matching on Display - while an in-market category behaves the same everywhere it serves.

03

Custom segments are editable and therefore debuggable, while an in-market category is take-it-or-leave-it, which changes what an optimization cycle looks like.

04

Competitor URLs in a custom segment reach people whose browsing resembles that site's audience, not the site's actual visitors, while in-market has no competitor dimension at all.

05

Custom segments replaced the older custom affinity and custom intent tools, so one segment can sit anywhere from loose interest to sharp intent depending on inputs, while every in-market segment sits at a fixed intent depth chosen by Google.

Which one should you use?

Use Custom Segments when

  • Your product is a niche with no matching in-market category, or the closest category is a level too broad.
  • You have Search query data that converts and want to chase those same searches into YouTube or Demand Gen.
  • You want to reach people who browse competitor or industry publisher sites, accepting that this means similar audiences rather than actual visitors.
  • You sell into a profession or vertical better described by the sites and tools it uses than by any shopping category.
  • You are willing to maintain and prune input lists as part of routine optimization.

Use In-Market Audiences when

  • Google's catalog has a category that genuinely matches what you sell.
  • You want an intent layer on Search campaigns, which custom segments cannot provide.
  • You need a fast setup with no list curation and no maintenance burden.
  • You prefer a stable, Google-maintained definition over a segment that shifts as inputs are reinterpreted.
  • You are comparing several categories for fit and want clean segment-level reporting rows to decide with.

Common questions.

Do custom segments with competitor URLs target that competitor's visitors?

No. Google uses the URLs to model people whose interests and browsing resemble that site's audience, not people who actually visited it. Actual visitor targeting requires your own tag on the site, which you only have for your own properties. Treat competitor URLs as a lookalike-of-their-audience signal, not conquesting in the literal sense.

Can I use custom segments on Search campaigns?

No. Custom segments apply to Display, Video, and Demand Gen only. On Search, your audience options include in-market, remarketing, and Customer Match layers, which is one of the practical reasons in-market stays relevant even when a custom segment outperforms it elsewhere.

Why did my custom segment's performance drift when I changed nothing?

The segment is rebuilt continuously against live behavior, so its membership shifts even when your inputs do not. Seasonality moves what people search and browse, and Google's interpretation of your inputs can tighten or loosen over time. If drift is material, split the segment into tighter single-theme versions so you can see which input group moved.

How many keywords should I put in one custom segment?

Enough to describe one theme and no more. The practical failure is not list length but mixed themes - packing brand terms, generic terms, and competitor terms into one segment gives Google a contradictory seed and you a segment you cannot diagnose. One theme per segment keeps every input pulling in the same direction and makes comparisons between segments meaningful.

Or stop choosing between them.

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