Retargeting

Retargeting is the practice of showing ads to people who have already interacted with a business: they visited the website, opened the app, watched a video, messaged the Facebook page or are on the customer list. Vietnamese media buyers often call it “chạy lại tệp”, literally “running the audience again”.

What is retargeting?

Instead of finding new people by age or interests, retargeting uses traces you collected yourself: a pixel or tag on your website, an SDK in your app, engagement on the ad platform itself, and the email addresses and phone numbers customers gave you. All of these count as first-party data.

On Meta, these audiences are called custom audiences. They can be built from your website (through the Meta Pixel), your app, your product catalog, a customer list, or people who watched a video, opened a lead form or engaged with your page on Facebook, Instagram or Threads. Each ad account can create up to 500 custom audiences (Meta Business Help Center, About custom audiences, accessed October 2026). Website visitors stay in an audience for anywhere from 1 to 180 days, depending on what you set (Meta for Developers, Website Custom Audiences, accessed October 2026).

Google Ads has replaced the word “remarketing” in its interface with “your data”. This group covers website visitors, app users, YouTube channel viewers, Customer Match lists and people who submitted a lead form (Google Ads Help, About your data segments, accessed October 2026).

Retargeting vs remarketing

In paid advertising, the two words are used almost interchangeably. The difference is in which channels people tend to attach each word to:

For apps, bringing lapsed users back has its own name: re-engagement.

Changes in 2025 and 2026 to know about

• Chrome is keeping third-party cookies. On April 22, 2025, Google said it would not roll out a separate prompt asking about third-party cookies; users choose in their settings, and Incognito mode still blocks these cookies by default (Privacy Sandbox, Next steps for Privacy Sandbox and tracking protections in Chrome, April 2025).
• Meta doesn’t recommend turning on Advantage+ audience for retargeting campaigns, because the feature lets the system find people outside the audience you selected (Meta, About Advantage+ audience, accessed October 2026).
• Meta flags and blocks custom audiences that contain disallowed information, such as a specific medical condition or a credit score (Meta, Understand restrictions on certain custom audiences, accessed October 2026).
• Vietnam’s Personal Data Protection Law No. 91/2025/QH15 took effect on January 1, 2026. Article 28 requires that behavioral or personalized advertising may only collect data through website and app tracking with the user’s consent, and that users must have a way to refuse sharing (Ministry of Public Security of Vietnam web portal, August 2025).

When browsers block the pixel, the Conversions API sends events from your server and doesn’t depend on cookies, though you still need the user’s consent.

Example (hypothetical)

A shoe shop in Ho Chi Minh City has about 3,000 people a month who add items to the cart without buying. The ad team splits them into three audiences: added to cart in the last 7 days (show the exact item they viewed, plus the shipping fee), viewed a product in the last 30 days (real customer review videos), and purchased in the last 180 days (excluded from the other two).

With a budget of 6 million VND a month and an assumed CPM of 60,000 VND, the shop buys 100,000 impressions. Spread across 3,000 people, that’s more than 33 impressions per person in a month, far too many. A small audience needs a correspondingly small budget, or the product-viewer audience needs to be folded in.

Frequently asked questions

Why is retargeting ROAS always high?

Because many people in the audience were already planning to buy. A high ROAS doesn’t tell you how many orders the ads actually added. To find out, hold back a control group that never sees the ads, the same approach used in incrementality testing.

Should you exclude people who already bought?

Yes, unless you sell products people buy repeatedly or have products to cross-sell.

If you want to review how your retargeting audiences and budget are split for your website or app, Adtek’s advertising team can talk it through via our contact page.