Contribution budget for summary reports

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.

# Engage and share feedback

You can participate and experiment with this API.

• Read about aggregatable reports and the aggregation service, ask questions, and suggest feedback.
• Read the Attribution reporting guides.
• Ask questions and join discussions on the Privacy Sandbox Developer Support repo.

# Next steps

• For more details on working with the contribution budget, refer to Scale up to contribution budget.
• For a review of other Attribution Reporting concepts, refer to Attribution Reporting system overview.