Smart bidding in Google Ads relies entirely on the quality of conversion data it receives. When you import GA4 conversions for smart bidding, subtle configuration errors can cause the algorithm to optimize toward the wrong goals or overvalue micro-conversions. This guide covers the exact setup required for reliable GA4-to-Google-Ads conversion import and the pitfalls that undermine smart bidding performance.

GA4 Import vs. Tag-Based Conversion Tracking

GA4 import uses GA4’s session-based attribution model rather than Google Ads’ own cookie-based attribution. GA4 import is preferable because it avoids double-counting when the same conversion is tracked by both GA4 and a Google Ads tag. However, GA4 import has up to 48 hours latency, making same-day reporting unreliable while the bidding algorithm accounts for it correctly.

Which GA4 Events to Import

Import purchase (or generate_lead for lead gen) as your primary conversion with a meaningful conversion value. Import all other events — add_to_cart, begin_checkout, sign_up — as secondary conversions for reporting only. Importing too many events as primary conversions causes smart bidding to optimize toward whichever conversion is most frequent, not most valuable.

Conversion Value Settings

Always use dynamic conversion values from GA4 purchase events rather than static values. Smart bidding with target ROAS requires actual revenue values. Verify in BigQuery that your purchase events include a non-zero value parameter. Static values make ROAS bidding meaningless — the algorithm cannot distinguish between a £10 order and a £1,000 order.

Attribution Model Selection

Set the attribution model to data-driven (DDA), which assigns fractional credit across all clicks in the conversion path. Data-driven attribution requires at least 300 conversions in 30 days. Below this threshold, use last click and switch to DDA when eligibility is reached. Avoid position-based or linear attribution with smart bidding.

The Conversion Window Setting

The window must match your actual customer journey. If 40% of customers convert within 60 days after clicking an ad but your window is 30 days, you are attributing only a fraction of conversions to Google Ads and causing smart bidding to underbid. Check your time-to-conversion data in GA4’s Monetization → Conversion paths report before setting this value.

Diagnosing Smart Bidding Problems

Compare Google Ads conversion volume against GA4’s own conversion count for the same period. They will not be identical due to attribution differences, but they should be within 20% of each other. If Google Ads shows 3x more conversions than GA4, you have duplicate tracking. If Google Ads shows 50% of GA4’s count, your import link may be broken or events are not passing the correct conversion identifiers.