One of the most debated topics in Google Ads bidding strategies is whether to use Target CPA (Max Conversions) or let Google optimise without a strict CPA limit.
To analyse this, I ran two campaigns—one with Target CPA and one without—to observe their impact on key performance indicators (KPIs).
The graphs attached show the differences in:
🔹 Search Lost Impression Share (Rank) – How often ads are not shown due to low Ad Rank
🔹 Search Lost Impression Share (Budget) – How often ads are not shown due to budget limits
🔹 Search Impression Share – The percentage of times an ad appears out of total available impressions
Key Observations & Behavioural Differences
1. With Target CPA (Max Conversions)
Google adjusts bids dynamically to keep the CPA within the set target. This creates efficiency but also trade-offs:
✅ Lower Lost IS (Rank): Since bids are adjusted strategically, the system ensures ads appear in auctions where the probability of conversion is higher, keeping rank losses minimal.
❌ Higher Lost IS (Budget): The algorithm skips auctions where the cost exceeds the CPA limit, leading to fewer impressions and budget underutilisation.
❌ Lower Impression Share: Because Google prioritises profitable conversions over maximizing visibility, many auctions are skipped, reducing the overall impression share.
2. Without Target CPA
When the CPA constraint is removed, Google bids more aggressively for clicks and conversions, leading to:
❌ Higher Lost IS (Rank): Since Google isn’t limiting bids to a target CPA, competition can push CPCs higher, sometimes causing rank losses.
✅ Lower Lost IS (Budget): Without CPA limitations, Google enters more auctions, reducing the chances of losing impressions due to budget constraints.
✅ Higher Impression Share: The campaign gets more visibility because Google is focused on maximising reach rather than filtering auctions based on CPA restrictions.
What This Means for Campaign Strategy
If efficiency and cost control are your priority, Target CPA ensures a better ROI but may limit reach.
If volume and market presence are more important, removing CPA limits can help maximise visibility but may lead to higher CPAs.
Hybrid Approach: A good balance is to start with Maximise Conversions, then switch to Target CPA once the campaign has enough data to optimise.
This experiment highlights the nuanced trade-offs between efficiency and visibility in Google Ads bidding strategies.
What has been your experience with Target CPA? Let’s discuss in the comments!
