Glossary
What is ios att tracking loss?
Melvin Salas1 min read
Short answer
iOS ATT (App Tracking Transparency) tracking loss is the gap between conversions that actually happened and conversions a platform can observe, caused by iOS users declining the tracking-permission prompt Apple requires since iOS 14.5. Declined users' activity is modelled or estimated rather than directly observed, which systematically under-reports true performance on iOS traffic and inflates apparent cost-per-result.
Since April 2021, every iOS app has to ask permission before tracking a user across other apps and websites for advertising purposes. Most users decline. For advertisers, this means a real share of iOS conversions become invisible to the ad platform's direct measurement: Meta's Aggregated Event Measurement and Google's modelled conversions are both attempts to estimate what's missing, not a substitute for actually seeing it.
The practical symptom: reported cost-per-result looks worse on iOS-heavy audiences than it should, purely from measurement gaps rather than genuinely worse performance. Comparing pre- and post-ATT performance directly, or comparing an iOS-heavy campaign's raw numbers against an Android-heavy one, both risk the same trap: reading a tracking artifact as a performance difference.
There's no full fix, since Apple's platform-level permission model isn't going away, but the standard mitigations are: lean on server-side/first-party conversion signals (Conversions API, Enhanced Conversions) where possible to recover some of the gap, hold a channel-level view of blended (not per-platform) true conversions from your own source of truth, and treat any iOS-specific CPA claim as directionally noisy rather than precise.
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