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Growth & Acquisition

Google Ads vs GA4: Why the Conversion Numbers Differ and How to Compare Them Fairly

Why GA4 and Google Ads report different conversions: date basis, models, windows, modelling and counting. A checklist for a fair like-for-like comparison.

· Zenko Protocol · 4 min read
Zenko fox compares a click calendar with a conversion calendar.
Illustrative artwork. Reporting settings and examples are explained in the article.

This page is part of Zenko's guide to marketing attribution discrepancies. It covers one pair of systems only: Google Ads and Google Analytics 4 (GA4).

The short answer is that the two products answer different questions with different default rules. Below are the differences Google documents, followed by a checklist for comparing them fairly. The sources used below were checked on 18 October 2026.

1. Date basis: click date or conversion date

Google Ads standard conversion reporting uses the date of the attributed ad interaction rather than necessarily the day the conversion happened (Understand your conversion tracking data). For comparisons with third-party systems, Google suggests the "All conv. (by conv. time)" column for a more comparable date basis.

Google's legacy migration article gives a worked case: a key event on 10 May linked to a click on 5 May appears on 10 May in Analytics and on 5 May in Google Ads (Possible reasons for conversion differences in GA4 vs. UA). That page is labelled Legacy and was written for the move from Universal Analytics, so treat it as an explanation of the date-basis principle, not as a statement of current GA4 behaviour. We did not find a current, non-legacy Google page comparing GA4 and Google Ads.

2. Attribution model and which channels can receive credit

Google Ads currently supports last click and data-driven models. Google says the first click, linear, time decay and position-based models are no longer supported and that affected conversion actions were upgraded to data-driven (About attribution models). The page shows no effective date, so check your account's change history.

In GA4, Google's page says the first click, linear, time decay and position-based models were removed in November 2023, and that changing the reporting attribution model affects both earlier and subsequent data in applicable event-scoped reports; user- and session-scoped traffic dimensions are unaffected (Select attribution settings).

GA4 also has a setting for which channels can receive credit in Google Ads reports. For Google Ads reports, the default is Google paid channels; for Google Analytics reports, it is paid and organic. The Google Ads setting can be changed to paid and organic, and the paid-and-organic option applies only to web conversions, as app conversions always use Google paid channels (same page). If one product credits only paid channels and the other credits a wider set, the counts will differ.

3. Lookback windows

Setting Google Ads GA4
Click-through or standard lookback Default 30 days; adjustable from 1 to 30, 60 or 90 days for Search and Display campaigns, depending on conversion source Acquisition key events (first_open, first_visit): 30-day default, 7-day option. All other key events: 90-day default, 30 or 60-day options
Engaged-view Default 3 days; adjustable 1 to 30 Not covered on the page read
View-through Default 1 day; adjustable 1 to 30 days or 1 to 4 weeks Not covered on the page read

Sources: About conversion windows and Select attribution settings (GA4 Help). These are the documented defaults, not a substitute for checking each conversion action in your own account.

Timing matters when you change a setting. In GA4, lookback-window changes affect subsequent reporting rather than rewriting earlier data. In Google Ads, a window change applies only to conversions from that day forward. Record the date of every change. For the cross-platform view, see how lookback settings move your numbers.

4. Modelled and cross-device conversions

Google explains that conversion totals can contain estimates, including cross-device modelling for outcomes it could not observe directly (Understand your conversion tracking data). With consent mode modelling, modelled conversions can be included in the conversion total and affect every report that uses conversion data. Eligibility requires consent mode or IAB TCF v2.0 to be implemented correctly, plus a daily ad click threshold of 700 ad clicks over a 7-day period, per country and domain grouping (About consent mode modeling).

This means a Google Ads figure may include conversions that no analytics tag recorded directly. Whether yours does depends on your consent setup and volume, so check rather than assume.

5. Counting settings

Google Ads can count every conversion or one conversion per interaction (Understand your conversion tracking data). If the two products count a repeat purchase differently, totals diverge even when both saw the same events.

6. Reporting lag

Google notes that some conversion reporting can lag by 24–48 hours (same page). Compare closed periods, not the last day or two.

What a gap of "up to 20%" means

Google's page says "Discrepancies, often up to 20%, are expected due to different attribution models" (Understand your conversion tracking data). That describes a common situation. It is not a tolerance you should adopt. Your acceptable gap is a decision for your team and finance partner, written down in advance.

A fair-comparison checklist

  1. Compare the same closed date range, avoiding the most recent two days.
  2. Use "All conv. (by conv. time)" in Google Ads when comparing against a conversion-date report.
  3. Confirm both products use the same conversion event, and write down how each defines it.
  4. Note the attribution model in each product and the date it last changed.
  5. Note lookback windows and the date of any change.
  6. Check whether the Google Ads figure includes modelled conversions.
  7. Check the counting setting (every or one).
  8. Check which channels can receive credit in the relevant Google Ads conversion report.
  9. Log the remaining gap and its likely cause in the ledger.

The ledger template is in the Attribution Disagreement Ledger.

What this page does not do

It does not say which product is right, set an acceptable gap, or prove which ads caused a sale.

Sources checked on 18 October 2026