Every major ad platform exposes the window as two dimensions: a click-through window (the time after a click within which a conversion is counted) and a view-through window (the same, but after an impression with no click). View-through credit is materially weaker as a causal signal — the ad rendered, the user took no action, and a conversion happened later. The window is a parameter of an attribution model, not a model in itself.
Defaults differ by platform and shift as platforms revise their measurement products. Click-window defaults have historically sat in the 7- to 30-day range; view-window defaults are typically around a day; both are configurable, on some platforms per conversion action. Check the current setting in the platform UI rather than relying on a memorized default — the same campaign reads differently across platforms because each is counting a different slice of time.
Two operator implications follow. First, window length should track the purchase cycle: impulse categories (apparel, beauty) tolerate shorter windows; considered-purchase categories (furniture, premium DTC) generally need longer ones. Second, window choice is an accounting choice — longer windows credit more conversions to a channel and raise apparent ROAS without changing the underlying outcome.
Each platform applies its own window with no cross-platform deduplication, so Meta-reported revenue plus Google-reported revenue commonly exceeds Shopify-reported revenue. That structural double-count is a reason MER, which is attribution-free, has gained ground on platform ROAS as a headline efficiency metric.