Two reports pull the same campaign and show different conversion counts, and the culprit is often invisible: the attribution window. It is one of the most consequential settings in analytics and one of the least understood. Here is what it is.

The core idea

An attribution window, or lookback window, is the period of time before a conversion during which a touchpoint is eligible to receive credit. If the window is 30 days, a click 29 days before the purchase can be credited, while one 31 days before cannot. The window draws the boundary of what counts as having contributed.

Why it changes your numbers

The window quietly decides how many conversions a channel appears to drive. A longer window credits more earlier touchpoints, which tends to favor upper-funnel channels that plant demand well before the sale. A shorter window credits only recent touches, flattering bottom-funnel channels. Change the window and the same data tells a different story, which is why mismatched windows are a frequent cause of reports that disagree.

The GA4 defaults

GA4 uses two default windows depending on the conversion:

  • Acquisition key events, like first visit and first open, default to a 30-day lookback.
  • All other key events default to a 90-day lookback.
  • Shorter options exist, so the window can be tuned per property.

Why it causes tool disagreements

Different tools use different windows by default, and that alone makes their conversion counts diverge. An ad platform set to a 7-day window and GA4 set to 90 days will credit different sets of conversions to the same campaign, with neither being wrong. Aligning windows is one of the first moves when reconciling numbers across tools, precisely because a window mismatch masquerades as a data problem.

How to set it deliberately

Because the window shapes the story, choose it to match your actual sales cycle rather than leaving the default unexamined. A business where people buy within a day is poorly served by a 90-day window that credits ancient touches, while a considered purchase with a month-long cycle needs a window long enough to capture the channels that started it. Set the window to the time it genuinely takes customers to convert, and keep it stable afterward so trends stay comparable.

A rule of thumb

When unsure, lean toward a window that spans a typical path to purchase and no longer, since an over-long window quietly inflates demand-creating channels while an over-short one erases them. The goal is a window that reflects reality, not one that happens to flatter the channel you like, and the honest test is whether you would defend the same window regardless of which channel it favored.

The attribution window is the invisible boundary deciding which touchpoints are young enough to earn credit, and it silently reshapes every channel number above it. Longer windows favor demand-creating channels, shorter ones favor closers, and tools that set it differently will never agree. Know your window, set it deliberately, and keep it consistent, and the setting that quietly caused your mismatched reports becomes one you control on purpose.

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