06 Aug Meta Custom Audiences vs Lookalike Audiences Explained
If you’ve been running Meta ads for a while, you probably fall into one of two camps on custom audiences: you think you know how to use them but you’re over-retargeting without realizing it, or you find the whole panel so confusing you avoid it entirely. Both are common, and both are fixable.
Here’s the one idea that makes everything else make sense: custom audiences are built from things you own.
Ownership is the whole concept
People regularly ask me if they can target visitors to a competitor’s website, or retarget a competitor’s customer list. The answer is no, and understanding why clears up almost every other question about custom audiences.
You can only put a Meta pixel on a website you own. Without that pixel tracking visits, there’s no way to build a website custom audience from that traffic. Same with a customer list — you can only upload and target people who are actually your customers. If you don’t own the asset, you can’t build an audience from it. Full stop.
This is also why lookalike audiences work the same way: you can only build a lookalike from an audience you already own. You can’t create a lookalike of your competitor’s customers, no matter how much you’d like access to that pool.
What counts as a custom audience source
Once you understand the ownership rule, the list of available sources is really just “everywhere you already have a presence”:
- Website visitors (via your Meta pixel) — general visitors, or specific actions like initiate checkout or purchase
- Customer list — a CSV upload of emails, phone numbers, or both
- App activity — for businesses with a mobile app
- Offline activity — in-store actions tied to a POS system, if you have that set up
- Video engagement — people who watched a certain percentage of your video content
- Instagram account engagement — profile visits, post engagement, message senders, saves
- Facebook Page engagement — page likes/follows, post engagement, message senders
- Lead form interaction — people who opened or submitted a lead form
- Event interaction — people who responded to, or attended, an event you ran
- Shop/catalog interaction — for businesses running Facebook or Instagram Shop
You don’t need a website to run meaningful retargeting. A Facebook Shop alone gives you enough interaction data — product views, adds to basket, checkout initiation — to build audiences without a single line of website code.
Retention duration: the concept most people get wrong
Every custom audience has a retention window, and it’s not what most people assume. If you’re targeting “people who visited my website in the last 30 days,” that doesn’t mean a fixed 30-day window for everyone — it’s rolling. Someone who visits today stays in the audience for 30 days from their visit. Someone who visits 15 days from now stays in the audience until 15 days after that.
It’s a first-in, first-out system. Once you understand that, the rest of custom audience management stops being confusing.
Retention windows vary by source, and it’s worth knowing the general ranges so you’re not guessing:
- Website/pixel, app (SDK), offline events: up to 180 days
- Video, Instagram, and Facebook Page engagement: up to 365 days
- Lead forms: up to 90 days
- Your own customer list: no expiration — it stays until you remove it
Lookalike audiences: built from your best custom audience, not all of them
A lookalike audience is Meta finding people who resemble a source audience you already own. The mechanics are simpler than custom audiences, but the strategy matters more than the setup.
Two things to get right:
Pick your source carefully. Not every custom audience is worth building a lookalike from. People who merely visited your Facebook page are a weak source. People who purchased are a strong one. A lookalike is only as good as the audience it’s modeled on — build it from your highest-intent data, not your largest pool.
Pick a percentage you’re comfortable with. A 1% lookalike is closer to your core audience but smaller. A 3% lookalike is broader and reaches more people, at the cost of some precision. There’s no universal right answer here — it depends on how much reach you actually need and how tightly you want to stay matched to your best customers.
You need at least 1,000 people in your source audience for Meta to build a meaningful lookalike. Below that, treat the audience as too thin to model from effectively.
The self-check before you build anything
- Do I actually own this asset? If the answer is no (a competitor’s site, someone else’s customer list), stop — it’s not possible on Meta.
- Am I picking a source based on quality or just size? A smaller high-intent audience beats a larger low-intent one for lookalikes.
- Do I understand this audience’s retention window, or am I assuming a fixed calendar period that isn’t how it actually works?
- Am I about to create a brand-new audience when I should be editing an existing one? (More on that in the next piece in this series — recreating audiences instead of editing them is one of the most common unforced errors.)
This breakdown is written by Jason Gan, a Meta Certified Professional and Badged Meta Business Partner who has personally audited over 1,000 advertiser accounts since 2010. You can see real account breakdowns on the Jason Gan YouTube channel.
Frequently Asked Questions
What’s the actual difference between a custom audience and a lookalike audience? A custom audience is built from people you already own — website visitors, your customer list, video viewers, people who’ve engaged with your page. A lookalike audience is a fresh set of people Meta finds because they resemble one of your custom audiences. You can’t build either one from someone else’s data — only your own.
Can I target people who visited a competitor’s website? No. Custom audiences only work on assets you own. You can only track and retarget visitors on a website where you’ve installed your own Meta pixel. If you don’t own the website, you can’t build an audience from its visitors, no matter how much you’d like to reach that traffic.
How many customers do I need before a lookalike audience is worth creating? Meta’s own benchmark is a minimum of 1,000 people in your source audience for a meaningful lookalike. Below that, treat it as a rough guide rather than a hard cutoff — but a custom audience with only a few hundred people usually isn’t a strong foundation to build a lookalike from.
Should I build a lookalike from every custom audience I have? No. Build lookalikes from your highest-quality audiences only — people who purchased, not people who merely visited your page. A lookalike built from your best customers will outperform one built from a low-intent audience, even though both are technically valid sources.
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