It's common to see discrepancies in conversion metrics between GA4 and Universal Analytics, and there are several reasons why this can happen. Here are the most common reasons for data discrepancies:
- Conversion window: Conversion window settings in Google Ads define how long after a Google Ads touchpoint conversion credit can be attributed to that touchpoint. A difference in settings between UA and GA4 can mean a touchpoint gets attributed conversion credit by one while it doesn't by the other.
- Fix it: Make sure your conversion window settings in Google Ads for the UA conversion actions are the same as what you've set for the GA4 conversions in the GA4 property settings.
- Attribution model settings: Attribution models determine how credit is assigned to different touchpoints in a conversion path. Different attribution models can result in different credit allocations across campaigns. Changing attribution settings in Google Ads does not affect the overall amount of conversions attributed to Google Ads in your Google Analytics account.
- Fix it: Ensure that the attribution models of the GA4 conversion matches the UA conversion in the conversion summary in Google Ads
- Conversion counting: UA counts one goal conversion per session, while GA4 often counts one conversion per event. Google Ads counts multiple conversions in a given date range. That means UA will only count one conversion per session whereas GA4 and Google Ads can count multiple conversions per session if there are multiple conversion events, which can result in differences in metrics.
- Fix it: To fix this, go to your conversion summary in Google Ads, find the conversion actions imported from GA4 and UA being compared and edit them to make sure that both conversions will have the same counting method: 'One conversion' or 'Every conversion' Learn more About conversion counting.
- To align GA4 counting to UA goals counting, make sure that the GA4 conversion counting method is set to 'Once' per session'.
Other reasons
- Auto-tagging: Hard-coded tag firing conditions can affect how and when a tag fires. If data collection is restricted in UA and not in GA4, then user, session, page view and conversion counts can be higher in GA4.
- Fix it: It's recommended you rely on gtag.js or gtm.js (using GA4 tags) to collect data for GA4 properties. Once tags are implemented, align any tag firing conditions.
- Site coverage: You may see measurement gaps if the UA tag is implemented on a different set of pages than the GA4 tag, especially if a landing page from a Google Ads ad isn't accurately tagged. If GA4 tags are implemented on more or fewer pages than UA, GA4 will respectively show more or fewer users, sessions, page views and subsequent conversions.
- Fix it: To minimise discrepancies, use the same tag implementation methods for UA and GA4, such as Google Tag or Google Tag Manager. Consider past settings, such as cross-domain tracking. Use the Tag coverage summary to confirm tag implementation. Use the 'Tag coverage' summary to see which pages of your website have the Google tag installed.
- Filters: In UA, filters are applied at the View level and can affect the amount of conversions in Google Ads. GA4 works very differently in this regard: some filters can be recreated in GA4 (for example, internal traffic exclusion), while others require transforming data by modifying existing events (for example, Search and Replace or Custom filters).
- Fix it: Recreate filters in GA4 where possible and modify existing events to replicate UA custom filters.
- GA4 conversion counting method: UA counts one goal conversion per session, while GA4 often counts one conversion per event. That means UA will only count one conversion per session whereas GA4 can count multiple conversions per session if there are multiple conversion events, which can result in differences in metrics.
- Fix it: To align GA4 counting to UA goals counting, make sure the GA4 conversion counting method is set to 'Once' per session.
- URL parameter exclusions: In UA, conversions can be configured to exactly match a particular URL. In GA4, conversions are defined by events, and there are no URL parameter exclusions. This means that a conversion in GA4 could be triggered by a URL with many different versions, as long as the event is fired.
- Fix it: Confirm if URL parameter exclusions are used in UA to understand potential differences in GA4.
- Session timeouts: The session timeout setting determines how long a user's activity is considered to be part of a single session. The session counts in your Google Analytics 4 property may be lower than the session counts in your Universal Analytics property because GA4 does not create a new session when the campaign source changes mid session, while Universal Analytics does create a new session under that circumstance.
- Fix it: It's recommended that you rely on the default settings. If you changed session timeouts in UA, you should adjust this setting in GA4.
- Consent mode: Consent mode modelling is available in Google Ads, for advertisers who have imported Google Analytics conversions from properties implemented using gtag.js or Google Tag Manager. For analytics.js implementations, we don't offer conversion modelling in Google Ads imported Google Analytics conversions, since the consent state can't be defined accurately without having a gtag.js or Google Tag Manager implementation. If both UA and GA4 rely on tags compatible with consent mode, both can receive conversion modelling in Google Ads.
- Fix it: To compare UA and GA4 conversions, you need a consent mode-compatible tag type for both properties and have an advanced implementation to get modelling in Google Ads for both UA and GA4 conversions.
You can review this list of conversion discrepancies to understand where the differences stem from and how to bring GA4 conversion volumes more in line with UA’s.
