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About the _gac cookie

Google Analytics writes various cookies to keep track of the data associated with your users. Beginning September 2017, analytics.js started writing the _gac cookie to store campaign information in order to provide Google Ads with a more reliable way to measure the interactions customers have with your business. Analytics writes campaign information to the _gac cookie when a user opens a page on your site via a URL that employs Google Ads auto-tagging.

Cookie name and value

A separate cookie is written for each Analytics property.

The cookie name includes the property ID. For example:

"_gac_UA-123456-12" ("_gac_property ID")

The cookie value contains a version number followed by a timestamp, and campaign information in the form of the gclid value. For example:

"1.123456789.CM-a9evq8dFDGUNR8BpeUWxBZB" ("version number.timestamp.gclid value")

Cookie settings

You can modify the cookie name, domain, and expiry using the same cookie-field settings you use for other cookies written by analytics.js. Learn more

Cross-domain tracking

analytics.js sends the _gac cookie along with all cross-domain-tracking parameters unless cookie writing is disabled as outlined below.

Effect on data

Analytics

The _gac cookie does not affect Analytics data or the way the data appears in Analytics reports.

Google Ads

If you have auto-tagging enabled, Google Ads adds a unique parameter, the GCLID or “Google click identifier”, to your landing-page URLs.

Google Ads conversion-tracking tags on your website use the _gac cookie to obtain GCLID information when the user converts, which improves the accuracy of its conversion tracking. Learn more

While all Google Ads conversion-tracking tags read and send this information by default, the data is immediately discarded server side if the Google Ads account that owns the tag is not linked to the Analytics property that stored the data in the cookie.

If you do not want Analytics to set the _gac cookie, you can opt out by following the instructions in the next section.

How to opt out

gtag.js

To opt out, include the following line in your tracking code:

gtag('config', 'UA-XXXXX-Y', {'store_gac': false});

analytics.js

analytics.js sets the _gac cookie by default. To opt out, add the following line of tracking code:

ga('create', 'UA-XXXXX-Y', 'auto', {'storeGac': false});

Google Tag Manager

Use an existing published tag container.

1. Navigate to Fields to set > Tag Configuration.
2. To opt out, set storeGac to false.
3. Save the tag configuration.
4. Submit the tag.
5. Publish the container.

Legal notice

As always, make sure that you provide your users with clear and comprehensive information about data that you may collect on your websites, and, where required, get consent for the collection of that information.

* Nguồn: Google Analytics