The conversion window is the period of time during which a conversion is attributed to a prior interaction with an advert. If a customer takes three weeks to decide and the window is set to seven days, the campaign that brought them in at the start receives no credit and looks ineffective. The budget then shifts towards channels that merely pick up customers who have already decided. Derive the length of the window, therefore, from the actual decision-making time in your industry – for fast-moving consumer goods, days are enough, while for more expensive services and B2B it is weeks to months. When comparing periods, bear in mind that the most recent days are not yet closed and the figures will still grow, so evaluating a campaign's result immediately after it ends means underestimating it.
See also: Offline conversion import, Incrementality, Data quality in analytics.
