Attribution windows
Change the attribution window and the exact same campaign can look like a winner or a loser. The window is how long after a click or a view a conversion still counts, and Meta compressed it hard after iOS 14.5's ATT framework. If you do not know which window you are reading, you do not actually know your results.
Current options
1-day click, 7-day click, 1-day click + 1-day view, and 7-day click + 1-day view (the default).
Attribution windows are set at the ad-set level, not the account level. They used to be account-wide.
28-day click and 7-day view are no longer available in the UI. The Comparison Window tool can show longer historical data for reference.
How we got here
Pre-iOS 14.5, the default was 28-day click + 1-day view.
January 19, 2021: Meta shortened the default to 7-day click + 1-day view in preparation for iOS 14.5.
Post-ATT enforcement in April 2021, new campaigns briefly defaulted to 7-day click only due to view-through signal loss.
September 23, 2021: default restored to 7-day click + 1-day view, where it remains.
iOS limitations
iOS users who opt out of App Tracking Transparency receive only Aggregated Event Measurement (AEM) attribution. AEM is limited to a single highest-priority event per user journey.
View-through attribution is unreliable on iOS. Most view-through conversions from ATT opt-outs are not reported at all.
Meta typically underreports conversions versus server-side analytics by 15 to 30 percent, sometimes up to 50 percent on iOS-heavy audiences.
Gotchas
Switching the attribution window on an ad set does not change historical reported conversions. It changes future delivery optimization and the current report view.
January 12, 2026: 7-day-view and 28-day-view windows were removed from the Ads Insights API entirely.
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