An attribution window, or lookback window, is the period after an ad interaction during which a resulting conversion is credited to that ad. Meta's default is a 7-day click window, meaning a conversion counts if the person clicked within the previous seven days; shorter windows or view-through windows credit fewer or different conversions.
Why the window changes the number
The same campaign will report more conversions on a 7-day-click window than a 1-day one, simply because it captures more of the delayed conversions common in considered purchases. Comparing two platforms, or two date ranges, without matching windows produces differences that look like performance changes but are just accounting.
Click vs view-through
A click window credits conversions after someone clicked the ad; a view-through window credits them after someone merely saw it. View-through inflates apparent performance and is the first thing we separate out when a channel's numbers look too good. As with every platform count, we reconcile back to the CRM's first-touch record rather than trusting the window-based number outright.