Every exposure carries its own 30 days. A conversion is attributed if it happens within 30 days of the moment that device passed your unit. That is the rule the report uses, and it is the one to reconcile a number against.

Per device, from the moment of exposure. Not from the campaign start, and not from the campaign end.

Take a flight running the 1st to the 28th of March. A device exposed on the 2nd has until the 1st of April for a conversion to count. A device exposed on the 28th, the last day, has until the 27th of April. Two devices on the same campaign, two different closing dates, because each one starts its own clock.

There is therefore no single date on which the campaign's counting stops. If you are reconciling a number in your report, this is the rule to reconcile against: find the exposure, add 30 days, and every conversion inside that span belongs to it.

The same rule applies to web, app, and footfall. There is no separate footfall clock.

Thirty days is the default, and it is a setting on your report rather than a platform constant. Almost every report runs at 30. A longer window can be configured where a purchase cycle genuinely warrants it, and if yours was set up that way you agreed it with your account team. If the arithmetic on a number does not work at 30 days, ask what your report is set to before concluding the report is wrong.

A second thing is true at the same time, and it is worth stating separately because the two get merged constantly.

We keep collecting conversion events until 30 days after your last unit goes dark. In the example above that is the 27th of April, because the people exposed on the final day still have their own 30 days to run. That is why your report is still moving weeks after the campaign ended.

What it does not mean is that the device exposed on the 2nd of March has until the 27th of April. That exposure closed on the 1st of April. The collection period is the outer envelope around every individual window; it is not a window of its own.

If you have heard the window described as 30 days after the campaign ends, this is the thing being described. It is a fair shorthand for why results keep updating, and it is not the matching rule.

OOH does have long-tail effects, and sales genuinely do appear after 30 days. That much is not in dispute.

The problem is detection. Lift in the long tail is smaller and spread thinner, so extending the window adds background noise faster than it adds signal. Pushed far enough, a longer window understates in-campaign performance by diluting a real effect into a much larger denominator.

Thirty days is also long enough for most considered purchases to land. B2B conversion times average around three weeks, which is the specific reason a two-week window is too short even though it gets quoted.

Then attribution is the wrong study. Causal lift measures against a counterfactual built from your own history, so a longer post-period is a modeling choice rather than a matching window. That is where to take this question.

Data for causal lift and halo effects is due about two weeks after the campaign ends, though causal lift can start mid-flight once two weeks of in-flight data exists.

Attribution needs nothing from you after launch.

Results begin populating around five days after campaign start. Treat anything faster as a bonus rather than a plan. Digital units lag further, because their exposure depends on operator play logs arriving.

Myth: The campaign gets one 30-day window that starts when the campaign ends.

Reality: Each exposure carries its own 30 days. The campaign end date only determines when collection stops.

Myth: A longer window would show more conversions, so this one undercounts.

Reality: It would also add noise. Smaller long-tail lift is harder to detect, so a longer window can understate performance.

Myth: Footfall uses a different, longer window than web.

Reality: All three attribution studies use the same per-exposure rule and the same window as each other.

Myth: Thirty days is a fixed platform rule.

Reality: It is the default, and it is set per report. A longer window can be configured where the purchase cycle warrants it.