Contribution budget for summary reports

Learn about the role of the contribution budget for Attribution Reporting summary reports and how to allocate it to capture the data you need.

To protect user privacy, individual users' contributions must have an upper limit.

In practice, this works as follows: across all aggregatable values associated with a single source (ad click or view), no value can be higher than a certain cap. We refer to this value as the CONTRIBUTION_BUDGET.

Contribution budget current value

In the explainer, the contribution budget is referred to as the L1 budget. L1 budget = CONTRIBUTION_BUDGET.

At the time of this writing, CONTRIBUTION_BUDGET = 2^16 = 65,536. The value of the contribution budget is arbitrary. What's important is that you can use this budget to maximize signal-to-noise ratio on the summary values.

The contribution budget applies across all metrics on a single source event (ad click or view event). The sum of all aggregatable values associated with the conversion(s) attributed to a given ad click or view (source) should be under the budget.

Implications of the hard cap

The contribution budget is a hard cap. Once the contribution budget is reached, no additional values are recorded.

This has a few implications. For example:

  • For the same ad click or view (source), the sum of all aggregatable values across all conversions should be at most 65,536 (CONTRIBUTION_BUDGET). If, for a given ad click or view, all the contribution budget is spent on the first five conversions, and a sixth conversion happens, that one won't generate a report.
  • For a single conversion event (trigger), the adtech company can register an aggregatable value of at most 65,536 (CONTRIBUTION_BUDGET). If the aggregatable value for that single conversion exceeds this budget, the aggregatable report is not created.
  • For a single conversion event (trigger), the adtech company can register multiple aggregatable values, and their sum should be at most 65,536 (CONTRIBUTION_BUDGET). If the sum of all aggregatable values for that single conversion exceeds this budget, the aggregatable report is not created.

Tips for success

These tips will help you work successfully with the contribution budget.

  • Ensure your values are strictly within the contribution budget to not lose any information, since the budget is a hard cap.

  • Allocate the contribution budget across metrics. Because the budget is common to all metrics for a given source, if more than one metric is tracked, you should share the budget across these metrics.

  • If you're tracking two metrics—for example, the purchase value and the purchase count—you would split the contribution budget across these two metrics. More details can be found in this example.

  • Adjust aggregatable values to minimize the impact of noise. Because the contribution budget impacts noise, adjusting the aggregatable values to this budget will allow you to improve signal-to-noise ratio. Read the details in Scale up to contribution budget.

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