What is an attribution (lookback) window?
An attribution window, or lookback window, is the period during which a click or view can still get credit for a later conversion. Set it to 1 day and only same-day conversions count; set it to 30 and a sale a month after the click still credits the ad.
Why it exists
People rarely buy the instant they click. The attribution window defines how long after an ad interaction a conversion can still be attributed to it. It is the time dimension of attribution: not which touch, but how long the touch keeps its claim.
Why it changes your numbers
- Longer window: more conversions credited to ads, higher reported ROAS, but more risk of crediting a click that was not really the cause.
- Shorter window: fewer conversions credited, more conservative, but you may undercount genuinely ad-driven sales with longer consideration times.
This is a big reason two platforms disagree: a 7-day-click Meta window naturally claims more than a 1-day one, feeding into Meta vs Google Ads conversion gaps.
How to set it sensibly
Match the window to your real buying cycle. An impulse-buy ecommerce store can use a short window; a high-consideration B2B purchase needs a longer one or you will massively undercount. Keep windows consistent when comparing periods, and remember that changing the window changes history, so a sudden ROAS shift can simply be a window change, not a performance change.
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