Advertising ID (IDFA and GAID)

What is an Advertising ID?

Every mobile device has an advertising ID. It is a string of letters and numbers, unique to that device, that gives advertisers a way to understand user behavior across apps without needing access to personal data like names, email addresses, or phone numbers.

Think of it as a pseudonym for your device. Advertisers can see what a device does, which ads it responds to, which apps it uses, and how it behaves after an install, without ever knowing who the person behind the device actually is.

For mobile marketers, advertising IDs are the foundation of user-level attribution, retargeting, and campaign optimization. They are what makes it possible to connect an ad impression to an install, and an install to downstream in-app behavior.

Types of Advertising IDs

There are three main advertising IDs used across the mobile ecosystem:

IDFA (Identifier for Advertisers)

Apple's advertising ID, used on iPhone and iPad devices. IDFA is assigned by iOS and can be accessed by advertisers when a user grants tracking permission through the ATT (App Tracking Transparency) prompt. It is the primary identifier for iOS attribution and targeting.

GAID (Google Advertising ID)

Google's equivalent for Android devices. The Google Advertising ID works similarly to IDFA, providing a resettable, anonymous identifier that advertisers can use to track activity and serve personalized ads across Android apps.

Amazon Advertising ID

Amazon's own advertising identifier, used within the Amazon ecosystem and on Fire OS devices. Less widely referenced than IDFA or GAID but follows the same core principles.

What Are Advertising IDs Used For?

When properly set up and consented to, advertising IDs give marketers access to a detailed picture of user behavior at the device level. This includes:

• Attribution: Connecting an install or in-app event back to the specific ad that drove it
• Retargeting: Reaching users who have previously interacted with your app or ads
• Audience segmentation: Building and targeting specific user groups based on behavioral data
• Campaign optimization: Using individual user data to improve bidding, creative, and targeting decisions
• Frequency capping: Making sure the same user does not see the same ad too many times

All of this happens without exposing personal information. The advertising ID is the bridge between user-level insight and user privacy.

How to Find Your Mobile Advertising ID

Finding your advertising ID depends on your device:

On iPhone (IDFA)

Go to Settings, then Privacy and Security, then Tracking. Note that since ATT, the IDFA is only accessible to apps you have granted tracking permission to.

On Android (GAID)

Go to Settings, then Google, then Ads. Your advertising ID is displayed here. You can also reset it or opt out of personalization from the same menu.

How to Reset Your Advertising ID

Both iOS and Android allow users to reset their advertising ID, which generates a new identifier and breaks continuity with any previous tracking data tied to the old ID.

On iPhone

Go to Settings, then Privacy and Security, then Tracking. You can manage which apps have permission to track, and reset your advertising identifier from here.

On Android

Go to Settings, then Google, then Ads, then Reset Advertising ID. From Android 12 onwards, users also have the option to delete their advertising ID entirely.

Resetting an advertising ID is useful for users who want a fresh start with their ad experience. For advertisers, a reset means losing the behavioral history associated with that device.

How to Turn Off Advertising ID Tracking

On iPhone

Apple's ATT framework means users are asked for consent on a per-app basis. You can revoke tracking permission for individual apps in Settings under Privacy and Security, then Tracking.

On Android

Go to Settings, then Google, then Ads. From here you can opt out of ads personalization. On Android 12 and above, you can delete your advertising ID entirely, which prevents any app from accessing it.

Advertising IDs in the Post-ATT World

The introduction of App Tracking Transparency (ATT) in iOS 14.5 fundamentally changed how IDFA works. Before ATT, IDFA was accessible by default unless a user had switched on Limit Ad Tracking (LAT). After ATT, the default flipped. Users now have to actively opt in before an app can access their IDFA.

The result is that a significant portion of iOS users are now unmeasurable at the individual level through IDFA alone. For many apps, opt-in rates have settled well below 50%, meaning the majority of iOS users generate no IDFA signal for advertisers to work with.

This has had a real impact on mobile marketing, pushing the industry toward privacy-preserving alternatives and aggregate measurement frameworks.

A practical tip for improving ATT opt-in rates: because Apple only allows the native ATT prompt to be shown once per device, many developers use a custom pre-prompt to set context before the native popup appears. A simple message explaining that opting in helps support a better ad experience, followed by the native ATT prompt, tends to perform better than showing the system dialog cold.

SKAdNetwork: Attribution Without IDFA

For iOS installs where IDFA is not available, Apple's SKAdNetwork framework provides a privacy-preserving alternative. SKAdNetwork allows ad networks and developers to measure app install attribution without accessing individual advertising IDs, using aggregated, delayed conversion data instead.

It is a fundamentally different measurement model from IDFA-based attribution, but it has become an essential part of the iOS measurement toolkit since ATT changed the landscape.

Advertising IDs and Tenjin

Tenjin uses advertising IDs as a core signal for deterministic attribution on both iOS and Android. When a user's IDFA or GAID is available, Tenjin can match installs and in-app events back to specific campaigns with precision.

For users where advertising IDs are not available, Tenjin's measurement framework incorporates SKAdNetwork data and probabilistic methods to maintain as complete a picture of campaign performance as possible, even in a privacy-first environment.

Related Terms

• App Tracking Transparency (ATT)
• SKAdNetwork
• Limit Ad Tracking (LAT)
• Mobile Marketing Metrics
• Mobile Measurement Partner (MMP)
• Attribution