How do attribution windows affect my numbers?

Cherry Seed

Attribution windows determine how far back in time a platform looks when deciding whether an ad deserves credit for a conversion. Facebook's default window is 7 days after a click and 1 day after an impression — any purchase within that window gets attributed to the ad. GA4 uses a 30-day lookback with last-click logic. Google Ads applies its own configurable window, typically 30 or 90 days. Wider windows capture more conversions for each platform, meaning the same purchase can appear as a conversion in multiple systems simultaneously. According to Meta's measurement documentation, narrowing Facebook's window from 28-day to 7-day click reduced reported conversions by 20-30% for many advertisers — not because fewer sales occurred, but because fewer fell within the shortened counting period.

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An attribution window is a time boundary: if the conversion happens within the window after an ad interaction, the platform claims credit. If it happens outside the window, it does not. This seemingly simple parameter has an outsized effect on the numbers each platform reports.

Facebook offers configurable windows — 1-day click, 7-day click, 1-day view, 7-day view — and the default combination of 7-day click plus 1-day view captures a broad range of influenced purchases. A customer who clicks a Facebook ad on Monday and purchases the following Sunday appears as a Facebook conversion. The same customer's purchase appears in GA4 as a direct or organic conversion if they returned to the site by typing the URL or clicking a search result.

GA4's 30-day lookback with last-click attribution credits the most recent interaction. If the customer clicked a Google search result on Saturday and purchased on Sunday, GA4 credits Google organic. Facebook and GA4 are now both counting the same sale, each under a different source.

Google Ads adds a third layer. Its conversion window can extend to 90 days for some conversion types, and it may include modelled conversions for users who did not consent to tracking. A single order can legitimately appear as a claimed conversion in three platforms.

The practical consequence is that comparing raw conversion counts across platforms with different windows is meaningless. A 40% discrepancy between Facebook and GA4 may be entirely explained by window differences, not by data loss. The only way to assess true performance is to anchor analysis to a first-party source — your own transaction records — and use platform numbers as directional signals within each channel.

Cherry Seed

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