Google Analytics cookie usage on websites

This document describes how gtag.js uses Google Analytics cookies to measure user interactions on websites.

Overview

As a user navigates between web pages, you can use the gtag.js tagging library to record information about the page the user has seen (for example, the page's URL) in Google Analytics. The gtag.js tagging library uses HTTP Cookies to "remember" the user's previous interactions with the web pages.

gtag.js uses the _ga and _gid cookies to distinguish unique users, and uses the _gat cookie to throttle the request rate:

Cookie name Default expiration time Can be set? Description
_ga 2 years Yes Used to distinguish users.
_gid 24 hours No Used to distinguish users.
_gat 1 minutes No Used to throttle request rate.
AMP_TOKEN 30 seconds to 1 year No Contains a token that can be used to retrieve a Client ID from AMP Client ID service. Other possible values indicate opt-out, inflight request or an error retrieving a Client ID from AMP Client ID service.
_gac_<property-id> 90 days No Contains campaign related information for the user. If you have linked your Google Analytics and AdWords accounts, AdWords website conversion tags will read this cookie unless you opt-out. Learn more.

To overwrite the default expiration time of the _ga cookie, provide a different value for the cookie_expires parameter in your config:

gtag('config', 'GA_TRACKING_ID', {
  'cookie_expires': 31536000  // one year (in seconds)
});