Attribution Window

An attribution window is the length of time an ad platform will look back from a purchase and decide that an earlier ad click or view caused it. If the purchase falls inside the window, the platform counts it in that campaign's conversions and revenue. If it falls outside, the campaign gets nothing, even though the same ad may have started the journey.

It is not a measure of whether the ad actually caused the sale; it is only a rule about how long credit lasts. People often confuse it with Incrementality, which asks what would have happened with no ad at all. A window can widen your reported numbers without a single extra order existing.

You do not calculate an attribution window; you choose it, then read the conversions and revenue the platform reports under that setting. Windows are written as click and view pairs, such as 7-day click plus 1-day view. The honest comparison holds spend and window fixed across periods, so changes in reported ROAS come from the ads. The flattering version widens the window, or adds view-through credit, and reports the larger figure against the same spend as though performance improved.

ROAS and MER both read differently depending on the window you set, since ROAS uses platform-attributed revenue while MER uses total store revenue and ignores attribution entirely. Incrementality tests what the ads actually added, usually with a Holdout Group. Conversions API affects how many conversions are matched and reported inside whatever window you have chosen.