iOS ATT and attribution
App Tracking Transparency (ATT) is Apple's framework requiring an app to request user permission before tracking it across apps and websites owned by other companies, or accessing the device's advertising identifier (IDFA). When permission is denied, the IDFA is unavailable, which removed the deterministic identifier mobile attribution long relied on and pushed the ecosystem toward aggregated, privacy-preserving measurement.
What this means
ATT, introduced with iOS 14.5, requires apps to call the AppTrackingTransparency framework and obtain user permission before tracking them across apps and websites owned by other companies, or accessing the IDFA (Identifier for Advertisers). If the user declines, the app cannot access the IDFA and must not track across other companies' properties.
The IDFA was the deterministic key that mobile ad attribution used to connect an ad impression in one app to an install or purchase in another. Removing it for non-consenting users broke that deterministic chain at scale.
How attribution adapted
With the cross-app identifier gone for most users, mobile measurement shifted toward aggregated and privacy-preserving approaches: Apple's own SKAdNetwork for install attribution, modeled conversions to estimate what cannot be observed, and a heavier reliance on first-party, on-property measurement that ATT's prompt does not cover.
The net effect is less granular per-user mobile attribution and more aggregated reporting. Reading iOS campaign performance now means accepting coarser, partly modeled signals rather than the deterministic user-level paths that existed before ATT.
- ATT gates cross-company tracking and IDFA access behind opt-in
- Denied permission removes the deterministic IDFA key
- Measurement moved to SKAdNetwork, modeling, and first-party data
How it appears in analytics and logs
Gaps in deterministic mobile attribution on iOS reflect ATT-driven IDFA loss; what remains is largely aggregated or modeled, not user-level cross-app tracking.
Diagnostic use case
Understand iOS ATT when reconciling why mobile attribution coverage and per-user linking dropped, and why aggregated or modeled measurement replaced IDFA-based tracking.
What WebmasterID can help detect
WebmasterID measures first-party events on your own properties, which ATT's cross-company tracking prompt does not target, so first-party measurement remains intact as cross-app tracking shrinks.
Common mistakes
- Expecting pre-ATT user-level mobile attribution to still be available.
- Treating aggregated iOS reports as deterministic per-user truth.
- Assuming first-party measurement is affected the same way as cross-app tracking.
Privacy and accuracy notes
ATT is a consent prompt by design: tracking across other companies' properties requires explicit opt-in. This page is educational, not legal advice — confirm obligations with counsel.
Related pages
- SKAdNetwork attribution
SKAdNetwork (SKAN) is Apple's framework for attributing app installs and post-install conversions to ad campaigns without identifying the user or device. Instead of a deterministic identifier, it sends the ad network an aggregated, delayed 'postback' confirming a conversion happened, with deliberately limited campaign granularity and a conversion value of restricted resolution. It is the privacy-preserving backbone of iOS install attribution after ATT.
- Modeled conversions
Modeled conversions are conversions a platform estimates statistically rather than observes directly. When direct measurement is blocked — by missing consent, cross-device journeys, or privacy protections — ad and analytics platforms model the likely conversions from observable trends and aggregated data, and report them alongside observed ones. Understanding which conversions are modeled is essential to reading attribution honestly.
- Consent and attribution
Consent is upstream of attribution: under frameworks like the EU's GDPR and ePrivacy Directive, storing or reading identifiers for tracking generally requires the user's consent. When consent is declined or withheld, the touchpoints those identifiers would have recorded never enter the data, so attribution operates on partial paths. Understanding consent is therefore inseparable from reading attribution honestly.
- Privacy-first analytics
First-party measurement unaffected by cross-app tracking prompts.
Sources and verification notes
- Apple Developer — App Tracking TransparencyOfficial framework documentation for ATT and the tracking permission requirement.
- Apple — User Privacy and Data UseApple's definition of tracking and IDFA access requirements.
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.