An attribution window is the length of time after someone clicks or views an ad during which a later conversion can still be credited to that ad. If a customer clicks your ad on 1 March and buys on 20 March, a 30-day window counts the sale and a 7-day window does not. Depending on the platform, you will see it called a lookback window or a conversion window.
How an attribution window works
Each ad platform records the click or impression, then waits. If the same person converts before the window closes, the conversion is credited under that platform’s attribution model. Once the window has closed, the ad gets nothing, however much it influenced the decision.
The defaults differ, which is one reason the platforms rarely agree. At the time of writing (October 2026):
- Google Ads sets the window on each conversion action. Click-through conversions default to 30 days and can be set anywhere from 1 to 90 days. View-through conversions, from people who saw a display or video ad without clicking, default to 1 day.
- GA4 sets its lookback window under Admin, then Attribution settings: 30 days (or 7) for acquisition key events such as a first visit, and 90 days by default for all other key events, with 30 and 60 days as alternatives.
- Meta Ads sets the window on each ad set. The standard setting is 7 days after a click plus 1 day after a view, with shorter and click-only options available.
Google Ads also reports conversions against the date of the click, not the date of the sale, so the last few days in any report look worse than they will once late conversions arrive. That delay is called conversion lag, and it is the main reason not to judge a campaign on yesterday’s numbers.
Why it matters
The window should match how long your customers take to decide. A takeaway in Bristol goes from click to order in minutes, so almost any window will catch it. A wedding venue in the Cotswolds, or a kitchen fitter quoting several thousand pounds, may see weeks pass between the first click and the enquiry. If the window is shorter than that, the platform under-reports, Smart Bidding learns that the campaign does not work, and spend drifts away from the searches that were actually finding you customers.
A window that is too generous causes the opposite problem. A long view-through window credits an ad for sales from people who scrolled past it once and bought weeks later for unrelated reasons. Generous windows flatter every platform and push the sum of their reported conversions further from your real total.
Common mistakes
- Leaving the defaults in place without checking them against the real sales cycle length of your business.
- Comparing Meta with Google Ads without noticing that one counts views by default and the other mostly counts clicks.
- Changing a Google Ads conversion window and comparing the next month with the last as if nothing else had changed. The change is not applied to conversions already recorded.
- Judging a campaign on the last seven days when the window is 30 days and many conversions arrive late.
How to act on it
Find out how long your customers usually take. Your CRM or booking system will show the gap between first contact and sale for recent customers, and in Google Ads the Days to conversion segment shows how long converters took after their click. Set the click window to cover most of that gap, and keep view windows short unless you have tested that views genuinely drive sales.
Write the windows down alongside each platform’s attribution model, so anyone reading a report knows what is being counted. When you review performance, allow for lag: either compare periods that finished long enough ago for late conversions to arrive, or mark the most recent days as incomplete. Setting and checking windows per conversion action is part of routine Google Ads management.