How to use the Google Ads change history to diagnose performance shifts

The change history in Google Ads records every modification to your account - bid changes, budget adjustments, ad additions, keyword additions, match type changes, and automated bidding strategy updates. It timestamps each change and records whether it was made manually, by an automated rule, or by Google's own systems. When performance shifts unexpectedly, this record is where diagnosis starts.

How to access it

In Google Ads, go to Tools and Settings, then Change History. You can filter by account, campaign, or ad group level, by date range, and by change type. For a performance investigation, set the date range to include the period before and after the performance shift and look for changes that occurred at or just before the shift started. The correlation between a specific change and a performance change is rarely proof of causation, but it is a strong starting point for investigation.

The changes most commonly linked to performance shifts

Bidding strategy changes are the most frequent cause of significant performance movements. Switching from manual CPC to Target CPA, changing a ROAS target, or adjusting a target significantly will often trigger a learning period that temporarily disrupts performance. If the change history shows a bidding strategy change coinciding with a performance dip, the dip is likely the expected learning period effect rather than a structural problem.

Budget changes - particularly increases - can also trigger learning periods in smart bidding campaigns. A campaign that suddenly has three times its previous daily budget will re-optimise its bid behaviour, and the transition period can produce volatile results. The change history will show you if a budget change preceded a performance shift.

Automated changes you may not have noticed

Google's auto-applied recommendations, automated bidding adjustments, and ad serving algorithm updates all appear in the change history. Many advertisers are surprised to find changes they did not consciously make. Regularly reviewing the change history is a useful practice even when performance is stable - it keeps you aware of what the account is actually doing, not just what you intended it to do.

Using change history for accountability

For agency-managed accounts, the change history provides a record of what was actually done. If a client questions why performance changed in a specific week, the change history either confirms that a specific optimisation was made or reveals that nothing was changed - which itself tells you something about whether the performance shift was internally or externally driven.