Attribution window

An attribution window is the length of time after someone clicks or sees an ad within which a later conversion is still counted as caused by that ad. Every attribution model needs one, because without a cutoff a purchase made a year after an impression could technically be linked back to it.

Ad platforms typically define two separate windows: a click-through window, often the longer of the two, and a shorter view-through window for view-through conversions where the user never clicked. Both last-click attribution and data-driven attribution rely on a window to decide which Click ID or impression is even eligible for credit. A shorter window undercounts purchases with a long consideration cycle, such as B2B software or big-ticket retail; a longer one risks crediting ads that had little real influence on the decision.

Attribution windows matter because comparing campaigns measured on different windows produces numbers that cannot be reconciled, and because platforms summing conversions within their own windows routinely report more total conversions than a business actually recorded. Changing a window also rewrites historical performance retroactively, a frequent source of "why did last month's numbers change" confusion.