A Guide to Google Analytics User ID in Google Tag Manager

If you’re looking at Google Analytics user metrics you need to understand one thing: the number of users does NOT represent the actual number of people visiting your website. It’s the number of different browsers that were used to visit your website/shop/etc.

That’s because when a visitor lands on a page for the first time, Google Analytics assigns a unique Client ID for that visitor (by storing in a cookie). As the visitor progresses and continues navigating, that Client ID persists across pages and lets GA understand that it is still the same visitor browsing pages.

However, if that very same visitor switches to another device or at least to another browser on the same device, Google Analytics will store a new Client ID (because they are not persisted across devices). And that’s the main reason why your GA User metrics, by default, are inaccurate and too big.

So what can you do? You could use the User ID feature in Google Analytics in order to reduce the effect of same user + different browsers. And in this exact guide, I’ll show you how to use User ID in Google Tag Manager (including how to get the ID and how to send it over to GA). Additionally, I’ll share a bunch of techniques how to acquire the User ID as a variable in Google Tag Manager.

Table of Contents

• #1. What is User ID feature in Google Analytics?
• #2. Enable User ID features in Google Analytics
  • #2.1. Enable User-ID reporting
  • #2.2. Create a User-ID reporting view
  • #2.3. Send User ID with Google Tag Manager to Google Analytics
• #3. How to get User ID in Google Tag Manager?
  • #3.1. Not everything can be a User ID
  • #3.2. Method No.1: asking a developer to push the User ID to the Data Layer
    • #3.2.1. Storing the ID in a cookie
  • #3.3. Method No. 2: Fetch the User ID from the already existing cookie
  • #3.4. Method No. 3: JavaScript Variable
  • #3.5. Method No. 4: DOM Scraping
  • #3.6. Honorable mention: Fetch User ID from the URL
• #4. Update Google Analytics Settings Variable
• #5. Time to test:
  • #5.1. Check the Preview and Debug console
  • #5.2. Check with a browser extension
  • #5.3. Check GA real-time reports in a User-ID view
• #6. GDPR and visitor’s consent
• #7. User ID as a custom dimension
• #8. Final words

#0. Before we continue: this topic is explained in the Intermediate GTM Course

If you think that this blog post was too complicated and you prefer video material, enroll in my Intermediate Google Tag Manager course where you will learn various GTM tricks and how to set up useful features (just like User ID in GTM).

#1. What is User ID feature in Google Analytics?

User-ID lets you associate a persistent ID for a single user with that user’s engagement data from one or more sessions initiated from one or more devices (and, of course, browsers).

When you send Google Analytics an ID and related data from multiple sessions, your reports tell a more unified, holistic story about a user’s relationship with your business.

Not only will User ID make your general User Metrics more accurate but it will also unlock a new set of reports/data:

• It modifies the data in the Audience > User Explorer report (replaces the Client ID with your provided User ID)
• Unlocks the Audience > Behavior > User-ID Coverage report (where you can see how many visitors have the User ID assigned vs unassigned)
• Unlocks Audience > Cross-Device reports that show:
  • How devices are overlapping (e.g. how many users browse with desktop AND mobile devices)
    
  • Device paths (the idea is pretty similar to the Top Conversion Paths (in the Multi-Channel Funnel reports) but it shows what are the most popular device sequences among your visitors (e.g. first they browsed with the mobile device but eventually made a purchase on a desktop).
    
  • Acquisition devices (shows the originating device (that was used to initially land on your website) and whether that very same device was used to convert).
    

Keep in mind that the bullet points above apply only to the User-ID GA View (continue reading and I’ll explain what it is). But still, User ID feature makes User Metrics a bit more accurate even in non-user-id views.

#2. Enable User ID features in Google Analytics

There are three ingredients you need for this to work:

• Enable User-ID reporting in Google Analytics
• Create a view specifically for the data with the User ID
• Send a user ID with Google Tag Manager from your website/shop/etc.) over to Google Analytics

There are also some legal things you need to keep in mind but I’ll mention them a bit later in this guide.

#2.1. Enable User-ID reporting in Google Analytics

To do this, you’ll need to have Edit permission for the GA property.

Sign in to your Google Analytics, choose the property you want to edit and go to Admin. Then, in the Property column, click Tracking Info > User-ID.

• Read the User-ID Policy
• Agree to the User-ID Policy
• Click Next Step

After that, you’ll see a page with some instructions and codes. Skip this for now by clicking Next Step.

#2.2. Create a User-ID reporting view

In that very same Google Analytics property, create a new view. You can either do that by clicking the Create button in that very same wizard:

…or go to the Admin section, View column, and click Create. Enter the reporting view name, choose the time zone and under the Show User-ID Reports, set the switch to ON. Click Create.

Important: you can create multiple User-ID views in the same property (usual view limits apply) but you cannot convert standard views to User-ID views and vice versa.

#2.3. Send User ID with Google Tag Manager to Google Analytics

The third ingredient (send the Google Analytics User ID with Google Tag Manager) is a larger one. In fact, the largest chunk of this guide is dedicated only to that.

#3. How to get User ID in Google Tag Manager?

Sending User ID as an additional parameter to Google Analytics (with Google Tag Manager) is pretty easy. Getting/fetching it beforehand might be a challenge (depending on the nuances of your project). In this guide, I’ll mention several tips/techniques how you can get the User ID in Google Tag Manager and then forward it to Google Analytics.

Keep in mind that the majority of these techniques are not universal, meaning that some of them might work for you while others won’t. Their usefulness solely depends on a website you’re working on, your team, your client’s capabilities, etc.

#3.1. Not everything can be a User ID

It’s really important to understand that Google Analytics’ Terms of Services do not allow tracking PII (Personally Identifiable Information), such as Email Address, Social Security Numbers, etc. stored on their servers. The same principle applies to the User ID. Even if you use email addresses to identify users in your system/CRM/etc., you cannot use email as a User ID in GA.

However, you can still use less readable User ID from your system (that consists of random numbers, letters, etc.) e.g. 1234567 or 123aboasdb2234. These are acceptable User IDs that you can use in Google Analytics.

But you might say Hey, aren’t such IDs still PII? I can look that ID up in my CRM and still identify the visitor. 

Well, yes, you can. But GA allows that. Kind of a gray area but the industry aligns with it. So don’t panic and use them. To sum up:

• [email protected] – CANNOT be used as a User ID in Google Analytics
• 5239asbd923fade923da – CAN be used as a User ID in Google Analytics.

I think I made my point clear here. Let’s proceed to some cool stuff, getting User ID from somewhere and then using it in Google Tag Manager.

#3.2. Method No. 1: Asking a developer to push the User ID to the Data Layer

If your website has an authentication feature (login), then you can ask a developer to push the User ID to the Data Layer. You can hand him/her the following code:

If you’re working on a regular website (that refreshes the entire page when the user is navigating), then it’s preferred to have this code placed above the GTM container (that way, you’ll have it available even with the All Pages GTM trigger).

If you’re working on a Single Page Application, then the location of this code does not really matter. Also, the ‘event’ parameter is not required. But if it is implemented, you can use it as a trigger to track Login events.

Another useful thing would be to ask a developer to push the User ID every time a new page loads (I mean when the page entirely refreshes and the previous values in the Data Layer are wiped out). Then the code could look like this (placed above the GTM container snippet):

After a developer starts pushing the User ID to the Data Layer, get back to your Google Tag Manager account, go to the container of the website that you’re currently working on and enable Preview and Debug mode.

Now, head over to your website, refresh it (while being logged out of that website) and log in. After you successfully authenticate, a login even should appear in the Preview console. Switch to the Data Layer tab of the Preview console and keep looking for the userId parameter. It should contain some value (the actual User ID).

Even though the User ID is in the Data Layer, you cannot simply use it in your tags or triggers without actually turning that piece of information into a GTM Variable. That’s why you need to create a Data Layer Variable for that User ID.

Note: Data Layer Variable Name (the field that I’ve highlighted in the screenshot above) is case-sensitive. So if there is a userId (with the uppercase I) parameter in the Data Layer, you must also use the uppercase I in variable’s name (in GTM user interface).

#3.2.1. Storing the ID in a cookie

If you want to go one step further, you can store the User ID in a cookie. Simo Ahava has already posted a guide on this topic so I borrowed his idea. Here’s how it goes:

• A visitor logs in for the first time.
• A developer’s code pushes the User ID to the Data Layer
• A Custom JavaScript Variable checks if the User ID is in the DL and then stores it in a cookie. If the User ID is not in the DL, then the value of the Cookie will be used.
• Finally, send cookie’s value with every GA hit

First, create a 1st Party Cookie variable (it will read the User ID if it is stored in a cookie)

The Cookie Name field is also case-sensitive. Where did that cookie come from, you ask? Well, from nowhere, yet. It will be set by a JavaScript code snippet that is displayed below.

Custom JavaScript Variable (Variables > New Custom JavaScript) with the following code:

Keep in mind that if you named your variables differently rather than I did ( {{dlv – user id}} and {{cookie – user id}} ), you should also rename them in the script above.

So what this script does is that it checks whether the userId is present in the Data Layer. If yes, the script stores a cookie in a browser called userId. If userId is not found in the Data Layer, then the script will return cookie’s value (and that cookie already contains the userId). If userId isn’t found anywhere, the variable will return undefined and user ID will not be passed over to Google Analytics.

Now, let’s pass the User ID with every Google Analytics hit. Open your Google Analytics Settings Variable and then click More Settings > Fields to Set. Enter the following values:

If you named the Custom JavaScript Variable differently, then use that name in the value field.

P.S. According to Google’s User-ID policy, you must not session stitch authenticated and unauthenticated sessions of your end users unless your end users have consented to such activity, and such merger is allowed under applicable laws and regulations.

In other words, if you plan to store the User ID in a cookie and track even unauthenticated users/visitors with the ID, then you need to get their proper consent (and also double check with your legal team and local laws if that is ok).

So if you managed to ask a developer to push the User ID to the Data Layer and then created a variable for it (and, additionally, created a mechanism that stores the ID in a cookie), you’ve done the large part of the task. Feel free to skip to Chapter #4 of this guide where I’ll show you how to use that User ID in Google Tag Manager tag (Google Analytics).

#3.3. Method No. 2: Fetch User ID from the already existing cookie

There’s a chance that a website/shop/etc. that you’re working on already stores the User ID in a cookie. In that case, you could just read its value with Google Tag Manager and then (later) send it over to Google Analytics. If you have direct access to the developers of that website/shop/etc., ask them whether they store the User ID in a cookie and what is its name.

Otherwise, you can check this hypothesis by yourself. Go to your browser’s developer tools. I’m using Chrome so I’ll go to More Tools > Developer Tools.

Then go to Application > Cookies and choose the domain of your website.

Now browse and keep looking for a name that might be related to a User ID. There is no standard name for that thus various options are possible. Once you find something, it would be good to ask the client/colleague to confirm whether that’s the actual User ID.

So if you got lucky with the cookie (insert your fortune cookie pun here), memorize its name and go to Google Tag Manager UI > Variables > New (under the User-defined variables). Choose variable’s type, 1st Party Cookie and enter the name of the cookie here:

So if this User ID fetching method worked for you, Feel free to skip to Chapter #4 of this guide where I’ll show you how to use that User ID in Google Tag Manager tag (Google Analytics).

#3.4. Method No. 3. JavaScript Variable

I’ve explained this technique in a dedicated blog post so if you want to learn more, go check it out. Here’s a quick summary.

In short, JavaScript variable lets you access values of global JavaScript variables available on that page. For example, a browser language, the title of the current page, etc.

I’m not sure whether it’s always possible (pardon my limited programmer knowledge), but I’ve seen many cases where the User ID was also stored in a Global JavaScript Variable. So all you need to do is to find it.

How do you do that?

• Option A: ask a developer who is involved with that website/shop/etc.
• Option B: try to find it yourself.

Option A is easy and should always be your first choice.

Option B requires much more time. To start the search, go to the developer console of your browser (here’s the tutorial on how to do that on Chrome), type window and hit enter (like in the screenshot below).

Click the black triangle near the Window and you’ll see a list of properties that we’ll be able to access with a JavaScript Variable in GTM. Brace yourself, that list will be huge.

Now, let’s imagine that you’re working with a Shopify online store. Intuitively, I’d scroll down and start looking for a shopify property. To save you some time, I can say that shopify property does not contain the User ID, however, ShopifyAnalytics does (I just had to spend some time looking for it).

Click the black triangle to expand the property and dig deeper. Unfortunately, I don’t see an ID anywhere, but there are some other possibly useful data points. Let’s dig even deeper. If you go to meta > page, you’ll find the customerId. This is exactly what you were looking for.

Now, head over to Google Tag Manager interface > Variables > New > JavaScript Variable and enter the entire path from top to the both that you followed to reach that customerId (window is not required). The final value of the variable must be ShopifyAnalytics.meta.page.customerId (case-sensitive). Every level is separated by a dot.

Save the variable, refresh the Preview mode (in the GTM UI), then go to the page and refresh it too (make sure you’re logged in to that website/shop/etc. as a user/customer). In Preview console, to Variables and check whether your JavaScript variable returns an actual User ID. If not, check for spelling mistakes in your JS variable.

So if this User ID fetching method worked for you, Feel free to skip to Chapter #4 of this guide where I’ll show you how to use that User ID in Google Tag Manager tag (Google Analytics).

#3.5. Method No. 4. DOM Scraping

This option is riskier due to its fragility (especially in websites where developers constantly implement improvements/changes/AB tests in the frontend).

In a nutshell, DOM scraping is a method to get a value from the website’s document object model by, well, scraping it. So if you, as a logged in user, see your User ID displayed somewhere in the interface, you could fetch its value with help of DOM Variable or Custom JavaScript Variable in Google Tag Manager.

DOM Variable enables you to pick a website element and read its text or one of its HTML attributes (e.g. href, title, ID, etc.). You can pick an element by defining its ID (if such exists) or by using CSS Selectors. In order to make use of it, the knowledge of HTML and CSS Selectors is required. Also, be familiar with what DOM is in general.

There are millions of websites thus there might be millions of ways how that particular element is coded. If you’re lucky, maybe that element will have an ID:

In that case, it should be no brainer to use the DOM Variable with the following settings:

If there is no Element ID, you could then try to fetch the element based on its (and its parents’) CSS Classes.

That’s where the knowledge of CSS Selectors would come in handy. Speaking of the screenshot above, the user ID is a span element with the class username. Let’s pretend that we know that there are more elements on a page with the same class, thus we need to be more precise. This element is descendant of the li element with ID wp-admin-bar-my-account. We can use this in our CSS Selector:

The CSS Selector I’ve used above means that I’m targetting elements that have a CSS class username and are descendants of an element with an ID wp-admin-bar-my-account.

Just don’t forget that several items on a page might be caught by the same CSS Selector. That’s why you should use the document.querySelectorAll() method to make sure that you’re fetching only that element that contains the User ID. Read the tip #18 in this guide to learn more.

Custom JavaScript Variable is much more flexible but also is more difficult to use because you need to know JavaScript. You can write simple (or complex) JS functions that will return the desired value (including the User ID).

But even if you don’t know JS, there is still a solution, GTM Variable Builder. This Chrome extension enables you to easily create Custom JavaScript variables which retrieve values of particular website elements.

How does it work? Open JavaScript console in Chrome, highlight any element on a website and click extension’s icon. What you’ll get is the JavaScript function that should be used in a GTM Custom JavaScript variable.

Get this extension

After you copy that ready-made function, paste it to the Custom JavaScript Variable in Google Tag Manager. It’s also a good practice to check whether this solution actually picks up only that one website element that contains your User ID.

Copy the first code that was generated by the plugin and instead of querySelector type querySelectorAll and enter this code in browser’s console. Hit enter. How many elements are returned? If one, then you’re good to go.

As always, when you create a variable, refresh the Preview and Debug mode in GTM. Then refresh the website that you’re currently working on and check the debug console. If your newly created User ID variable displays the actual value, then everything is working properly. If not, then check your CSS Selectors.

Public Service Announcement: However, this “hack” should be always considered as a plan B. It’s always better to actually know JavaScript, DOM, CSS Selectors. It’s much better to talk with developers upfront and ask them to push the User ID to the Data Layer rather than try scraping the website.

You see, when you’re using DOM Variable with the CSS Selectors (or a Custom JS variable generated by the GTM Variable Builder), you’re telling Google Tag Manager the exact path to that website element in the entire website document (e.g. from its parents to that very exact element).

Now if that path changes anywhere along the way (due to developer’s input or something else), your CSS Selectors or Custom JS variables will break and return undefined. Meaning that your User ID tracking in Google Tag Manager will stop working.

Nonetheless, in most cases, scraping is better than having/doing nothing. But if there is a slight chance of talking with developers, PLEASE PLEASE PLEASE do that and cooperate with them.

You + Developer + Data Layer is an unbeatable trio in tag management.

Anyway, if this User ID fetching method worked for you, Feel free to skip to Chapter #4 of this guide where I’ll show you how to use that User ID in Google Tag Manager tag (Google Analytics).

#3.6. Bonus: Fetch user ID from the URL

Even if your website does not have a login, you might be sending a newsletter to your visitors/users. You could take the Contact ID of the subscriber (from your Email Service Provider (ESP)) and user it as a User ID in Google Tag Manager and Google Analytics.

I won’t go into details but here’s the main idea:

• If your ESP does not add Contact IDs in the URL when the subscriber clicks the link in your emails, then you could do that by yourself. Many ESPs support inserting attributes (a.k.a. Merge Tags) in emails and links. Benjamin from Loves Data mentions it in his video (@1:45)
• When the visitor lands on a page, you could read the URL, catch the Contact ID (with help of URL Variable) and later store it in a cookie (just like it was done in the chapter #3.2.1 of this guide). Just instead of the Data Layer Variable, you would be using URL variable.

But keep in mind that this option should also be considered as a plan B and it will work only for those visitors who are clicking your emails links with different devices.

#4. Update Google Analytics Settings Variable

Great. So far, we have enabled User-ID features in Google Analytics and learned several ways how to fetch the User ID in Google Tag Manager and turn it into a variable. Now we need to use it in our Google Analytics tags.

There are two ways: a bad way and a good way.

The bad way would be to update every Google Analytics tag in your GTM container and configure them to send User ID over to GA. I won’t even explain how that can be done because it is not the practice you should be following. By this day, you should have already migrated or come across to the GA Settings Variable.

The good way is to update your Google Analytics Settings Variable. Once you configure it to send the User ID, all Universal Analytics tags (that are using that variable) will automatically inherit that setting (unless you have done some exclusions on a tag level).

In your GTM container, go to Variables and choose the GA Settings Variable that you’re using in Universal Analytics tags. Expand More Settings > Fields to Set and enter:

• userId
• the variable (you have created in Chapter #3 of this guide) that returns the User ID. E.g if you chose the #3.2 method, then the possible name of the variable could be {{dlv – user id}}

The important thing here is that if you want to see every hit (events, page views, etc.) in the Google Analytics User-ID view, you need to pass the User ID with every hit. That’s why we’re configuring User ID on the level of the GA Settings Variable (and not just in the Pageview tag).

#5. Time to test

There are many options and tips but it’s fully sufficient to do the following:

#5.1. Check the Preview and Debug console

After you’ve updated the GA Settings Variable with the userId field, refresh the Preview and Debug mode, then go to the website you’re currently working on and reload the page. Then let’s check the Page view tag. Click Page view event in the left sidebar (or some other event upon which the Page View tag fires) and click the Universal Analytics tag.

Now scroll down a bit and check whether the userId field had the proper value. If not, there might be several reasons for that (depending on a method you chose to fetch the User ID.

Got undefined? If you got the User ID with the help of Data Layer Variable, it’s possible that User ID is not available yet on a Page view. Maybe a developer is pushing the User ID only after the DOM ready? Check that by clicking the DOM Ready event and going to the Variables tab. See if the value of your DLV is not proper. If yes, you should fire your Universal Analytics tag on DOM Ready instead of an All Pages trigger.

If you chose DOM Scraping, then the User ID will definitely not available with the Page view event. Fire your Universal Analytics Page view tag on DOM Ready trigger.

There are many reasons why your User ID variable returns an undefined value but the main idea here is that either you misconfigured a variable that fetches the User ID (e.g. spelling mistake) or that data is not available during that event yet. In the case of the latter, read this guide on how to properly debug with GTM(especially tip #8).

#5.2. Check with a browser extension (e.g. Tag Assistant or GA Debugger)

From what I’ve seen, the majority of GTM users (especially intermediates) use Tag Assistant or GA Debugger to test Google Analytics tracking. Let’ take a look how can you debug User ID in Google Tag Manager with these to extensions.

Tag Assistant. If you haven’t yet, install it here (P.S. here’s a more comprehensive tutorial). After you’ve installed the extension, a blue tag icon will appear in the top right corner.

By default, Tag Assistant is in the “sleep mode”, meaning that it does not check anything that’s happening on a page. In order to activate it, click the blue tag icon and then Enable.

Now refresh the page. If any of Google’s products are implemented on that page, you’ll start seeing a particular number within that blue tag icon which represents the count of tags found.

Click the blue icon again to see a detailed list of all found tags. Then choose Google Analytics to get more details about, you’ll learn what data was passed, what could be improved, how many events were fired, etc.

If User ID was implemented correctly, you’ll see the ID right here (after you choose Google Analytics). P.S. You might need to scroll down a bit in the Tag Assistant window to find the ID.

GA Debugger. Once installed and enabled, this extension enables GA’s debug mode that starts displaying the data in the browser’s JavaScript console.

To enable it, simply click the extension’s icon and you’ll see the ON ribbon. This indicates that the GA Debug mode is enabled and you can start checking the data.

Then open browser’s JavaScript console and refresh the page. You’ll start seeing all the requests that were sent to GA.

Even though the info might look a bit too technical, this is definitely worth checking out as it (more or less) clearly displays all the parameters that were passed to Google Analytics (including the User ID). Keep looking for the &uid in the table and check whether its value is correct.

By default, browser’s console is cleared every time the page reloads. So if you want to preserve what was captured, enable Preserve Log setting:

#5.3. Check GA real-time reports in a User-ID view

Last but not least, let’s check whether the data actually reached its destination, Google Analytics. To do that, go to your GA User-ID view’s Real-time reports. Not just any view’s RT reports but a view with User-ID tracking features enabled.

This view displays only those hits that contain the User ID (&uid) parameter. Do you see your pageviews in real-time? If yes, then the testing is complete.

If not (even though GTM Preview mode and browser extensions displayed everything correctly), read this guide that will help you troubleshoot problems in Real-time reports.

#6. GDPR and visitor’s consent

If you’re tracking traffic coming in from the European Union (regardless of your business location), your User ID setup in Google Tag Manager is not ready yet. That’s because your User ID tracking in Google Tag Manager is not GDPR-compliant. Yet.

In a nutshell, GDPR (General Data Protection Regulation) is a law that requires consent from a visitor/user in order to process his/her PII (Personally Identifiable Information). User ID falls under this definition too. This means that you can set the User ID in a Google Analytics Settings Variable only if a visitor/user agrees to that.

I will not go into details what GDPR is (there are other great blog posts out there like this one, this one or this one).

Back to the User ID and GDPR. There are many tools and guides on how to implement consent banners on a website with Google Tag Manager (including this one). Here’s a quick summary of how such mechanisms work:

• A visitor lands on a website
• A banner (asking for consent to track/process PII) pops up
• A visitor/user can agree or disagree to have his/her PII processed by your website/company
• That consent is then usually stored in a cookie (also, it’s pretty common to push the consent data from the website/web app) to the Data Layer and access it via Data Layer Variable

Let’s imagine that on a sample website when a visitor/user agrees to have his/her PII processed, this consent is stored in a cookie and its value can be accessed in GTM with the help of 1st Party Cookie variable called cookie – consent to process pii. Possible values of that variable can be true or false. Remember, this is all just an example. In your case, variables and cookie names can be totally different.

If the value of that cookie is true (means that the consent was given), we should automatically insert the User ID in a Google Analytics Settings Variable. If false, our User ID variable should not be passed to Google Analytics.

In order to achieve this, we’ll need to use Lookup Table Variable.

Lookup Tables (and Regex Tables too) are awesome because they return different outputs depending on the value of the input variable. In this case, we can configure it to return the {{dlv – user id}} only if the value of {{cookie – consent to process pii}} variable equals to true. In other cases, the output will be undefined.

Keep in mind that in the second row of the table I used the Undefined Variable. Because if you left the output field empty, it would return an empty string and we want here to send no value at all (read undefined). You can learn more about the Undefined Variable here.

Another important thing is that in your case, the User ID variable might be different (not {{dlv – user id}}. Maybe it is {{cookie – user id}}. It depends on the situation. My point here is that you should insert YOUR User ID variable as an output (on the first row) in a Lookup Table if the consent of a visitor equals to true.

Save the changes and test. If a visitor/user gave the consent to process PII, then your Lookup Table variable should return an actual User ID. If the consent was denied, then the value should be undefined.

Finally, open your Google Analytics Settings Variable and replace the previously inserted plain User ID variable with that Lookup Table.

Save and repeat all actions (of testing) listed in Chapter #5.

In addition to this setup, you should update your Privacy Policy. Unfortunately, I’m not the right guy to ask for advice here. Go and discuss this with your legal department.

#7. User ID as a custom dimension

As of the beginning of 2019, Google Analytics still does not allow to build segments based on a User ID so if you want to debug only one visitor’s actions, User ID (as a dimension) will not be available.

However, that’s not a problem because you can pass the User ID as a custom dimension (CD) to Google Analytics. Simo Ahava has mentioned this CD in this guide (tip #1.4).

Once again, you must respect visitor’s/user’s privacy preferences and pass the CD only if the consent was given (meaning that you should use a Lookup Table here too).

User ID in Google Tag Manager: Final words

We’ve finally reached the end. In this guide, I’ve explained how to properly implement Google Analytics User ID with Google Tag Manager. In short, the process goes like this:

• Enable the User-ID tracking features in Google Analytics + create a User-ID view
• Find the way how to get the User ID as a variable in Google Tag Manager. There are many ways and I’ve shared several of them:
  • Data Layer Variable (+ later store it in a cookie)
  • Read the cookie that is already created by the website/platform/shop/etc.
  • User JavaScript Variable
  • Scrape DOM
  • Parse the ID from the URL and then store it in a cookie
• Once you have the User ID as a variable in Google Tag Manager, set it as a userId field in Google Analytics Settings Variable.
• If you have some visitor traffic from Europe, you need to abide by the GDPR and respect visitor’s/user’s privacy preferences. This means that the User ID can be passed to Google Analytics only after the consent is given. For that, we used the Lookup Table Variable.

With User ID, you will be able to see cross-device data and how visitors use them on your website/shop/etc. This can tell you a whole new story. Also, User ID improves the accuracy of user metrics in GA (even in views without User-ID tracking features).

Don’t panic if your User metrics will decrease, that’s exactly what you should expect. By default, every device and even every browser is treated as a separate user. With User ID feature, several devices will turn into one actual user.

Have any questions regarding User ID in Google Tag Manager? Did I miss anything? As always, comments are at your service.

Also, if you prefer video content over text, feel free to enroll in the Intermediate Google Tag Manager course where one of the topics is User ID tracking (with GTM)