Making sense of GA4 and Google Tag Manager: A practical guide

Google Analytics 4 (GA4) is Google’s latest analytics platform, designed to give you a deeper and more flexible understanding of your website and app performance. It is not just a new version of Universal Analytics, it’s a completely reimagined platform designed for cross device tracking, event based measurement, and deeper insights into user behaviour. It enables more flexible, privacy conscious data collection and customisation.

• Measure traffic and engagement across your website from multiple sources such as paid campaigns, organic search, and social media platforms.
• Monitor specific user actions, including page views, scroll depth, video plays, and conversions.
• Create custom reports tailored to your business KPIs and marketing objectives.
• Combine insights with tools like Google Tag Manager to report on specific events and Search Console to get a clearer picture of website performance on organic search.
• Share meaningful performance data with your team or clients to support better collaboration and decision making.

Once GA4 is set up on your site, navigating its interface and knowing where to find the right information is essential. GA4 offers a series of built in reports that are grouped by topic and can be customised based on your needs.

Key report types of GA4 include:

• Real-Time Reports: Show what’s happening on your website right now, including active users and current pages being viewed.
• Acquisition Reports: Reveal how visitors arrive at your site, this could be through search engines, campaigns, direct visits, or social platforms.
• Engagement Reports: Show which pages are being viewed, how long users stay, and what actions they take.
• Monetisation Reports:  For e-commerce sites, focus on revenue and transaction data.
• Retention Reports: Compare behaviours of new and returning users over time.
• User Reports: Provide demographic and device data to help you understand who your visitors are and where they are visiting from.

In addition to these core reports, GA4 allows you to dig deeper by using the filters on existing reports or by navigating to the explore section, where you can build reports tailored to you. 

It’s important to remember that GA4 processes data differently than its predecessor, and many reports can take 24 to 48 hours to fully populate. So when you’re analysing data, allow for this delay and always ensure you’re looking at complete datasets.

Google Tag Manager (GTM) is a powerful tool that allows you to set up advanced tracking without having to change your website’s source code. It’s the bridge between your website and GA4, enabling you to track user interactions with precision. GTM works through:

Tags: Code snippets that send specific data to GA4 when users take an action, like clicking a button or submitting a form.

Triggers: Rules that determine when a tag should fire (e.g. on a page view, scroll event, or successful form submission).

Variables: Pieces of information that tags and triggers rely on, such as button labels or page URLs.

One of GTM’s key components is the Data Layer, a JavaScript object that temporarily stores structured data about user interactions. This allows GTM to collect data from the website and use it to trigger tags or populate reports in GA4. The platform also helps with version control, showing you exactly what changes were made and when, which is useful for debugging or rolling back if needed.

Once the Google Tag Manager code has been added to the site by a developer, setting up custom tracking can be done entirely within GTM’s interface, below is an example for setting up a tag on GA4:

• Create a new tag (e.g., GA4 event).
• Set a trigger that specifies when the tag should fire (e.g., when the ‘Subscribe’ button is clicked)
• Define variables if needed (e.g., button text or form location).
• Use Preview Mode to test the setup, ensuring the tag fires under the right conditions.
• Once happy with the event, you can publish the GTM container. 

To support accurate testing, we recommend using browser extensions such as:

• Tag Assistant
• DataLayer Checker Plus
• GA Debugger

These tools help you debug and verify that your tags are firing correctly and passing data to GA4 as expected.

Not everything is tracked automatically in GA4. Using GTM, you can create events that give you more insight into how users are engaging with your website. By choosing meaningful actions to track, you can better understand how users move through your site and where improvements can be made. Popular actions to track include:

• Clicks on ‘Subscribe’ or ‘Register’ buttons
• Successful form submissions or newsletter sign-ups
• Logins and account registrations
• Social share button clicks
• Views of sponsored or high-value articles
• Page views categorised by content type (e.g., blog, product, news)

As privacy regulations like GDPR become more rigorous, it’s essential that your tracking setup respects user consent. Google’s Consent Mode V2 introduces a more granular approach, allowing for each tag to be configured based on the specific type of consent it needs; such as for advertising, analytics, or personalisation.

In GTM, you can:

• Assign consent settings for each tag (e.g., analytics_storage, ad_storage, etc.).
• Check how consent is being applied using GTM’s Consent tab in Preview mode.
• Ensure that your tags do not fire unless the correct level of consent has been provided.

If a user does not give consent, GA4 can still collect limited, non-personally identifiable data using what are known as “cookieless pings.” These include basic detail, this is enough to provide high-level insights while respecting privacy settings. Google has also introduced behavioural modelling, where machine learning is used to estimate user behaviour based on data from users on your site. This modelling requires your GA4 property to meet certain data thresholds, such as a minimum number of daily events from users who denied and granted consent.

To benefit from this, your GA4 property must:

• Use consent mode on all site pages
• Load Google tags before the consent dialogue appears
• Generate a sufficient number of events and users each day across both consented and non-consented groups
• This feature helps fill in gaps in your data and maintain visibility while remaining compliant.

As third-party cookies become less reliable and privacy-focused browsers become more common, businesses need alternative tracking methods that preserve insight without compromising compliance. Cookieless tracking via GA4 and GTM is one solution, but server-side tagging offers an even more robust approach.

Server-side tagging shifts the responsibility of data collection from the user’s browser to a secure server environment. This gives organisations more control over how data is collected, processed, and shared. This makes it especially valuable for industries like healthcare or finance, where data sensitivity is high.

Because server-side tagging avoids many issues caused by browser restrictions or ad blockers, it can also improve data accuracy, ensuring that valuable user behaviour insights aren’t lost. It’s a particularly useful option for websites that don’t have the traffic volume to meet GA4’s behavioural modelling thresholds, as it offers more reliable data capture without relying on cookie consent.

In summary the benefits of server-side tagging include:

• Greater data privacy and control—ideal for healthcare, finance, and legal sectors.
• Reduced data loss due to ad blockers or privacy browsers, which often block client-side scripts.
• Improved tracking accuracy even for sites with lower traffic volumes that may not qualify for GA4 behavioural modelling.
• By moving data processing to the server, your tracking setup becomes more resilient, secure, and reliable.

Whether you’re setting up analytics for the first time or refining an existing setup, GA4 and GTM provide the tools you need to understand your audience, measure performance, and drive smarter business decisions. From custom event tracking to consent management and cookieless solutions, these platforms can be tailored to your specific business needs; if you know how to use them.

At Varn, our Data team specialise in helping businesses get clarity from their data. If you’d like to review your current setup, implement better tracking, or explore server-side tagging options, send us a message as we are here to help.