Attribution Window

An attribution window is the rule that says how far back a platform will look to credit a conversion. If someone clicks a Meta ad today and converts five days later, whether Meta claims that conversion depends entirely on the window. A 7-day click window says yes; a 1-day window says no. Windows come in two flavors: click-through (the user clicked, then converted within X days) and view-through (the user merely saw the ad, then converted within X days). View-through windows are far more generous and far more contested — they credit ads nobody clicked. This is the single biggest mechanical reason "the numbers don't match." The exact same set of conversions gets counted differently because each platform applies a different window by default. Stretch a window and a platform's reported conversions rise; shrink it and they fall — without anything changing in the real world. Before comparing platforms or judging ROAS, you have to know which windows are in play. Two campaigns can look wildly different in efficiency purely because one platform is using a 7-day click / 1-day view default and another isn't.