Consent Mode: what disappears from your GA4 and Google Ads data

When a visitor declines cookies in your cookie banner, the visit disappears wholly or partly from Google Analytics 4 and Google Ads. That is how it should be. But it means the numbers in your reports are always lower than reality, and the gap depends on how consent is set up.

Consent Mode is Google's way of telling the tags on your website what the visitor answered in the banner. Tags are the small snippets of code that send data to Google. This post covers what is required in the EEA and how basic and advanced mode differ. Finally, I show you how to work out what is missing from your numbers.

My recommendation is that you use basic mode and work out how large a share of your purchases or enquiries is missing from your analytics. Then you know how to read the reports and avoid making decisions on numbers that look worse than they are. Basic mode is also what we use on our own website.

What is required in the EEA

The EEA is the EU member states together with Iceland, Liechtenstein and Norway. The consent requirement comes from the EU ePrivacy Directive, which each member state has written into national law. In Sweden it is the Electronic Communications Act. Cookies and similar technologies that are not needed for the website to work may only be used if the visitor has said yes. Cookies for analytics and advertising fall into that group.

Consent must be freely given and informed, and it must be as easy to withdraw as to give. The EU's data protection authorities work together in the EDPB, the European Data Protection Board. In a report from the EDPB's cookie banner taskforce, a large majority of the authorities considered that a banner breaks the rules if it has a button to accept but none to reject at the same level.

Google also has its own requirements. Under Google's EU user consent policy, advertisers must have consent for cookies where the law requires it and for personal data to be used for personalised ads. Since March 2024 Google also needs to receive that consent as signals for measurement and remarketing to work for visitors in the EEA. Remarketing means ads shown to people who have already visited your website.

Consent Mode sends four signals.

• ad_storage controls cookies for advertising.
• analytics_storage controls cookies for analytics.
• ad_user_data controls whether data about the visitor may be sent to Google for advertising.
• ad_personalization controls whether the visitor may see personalised ads and be added to remarketing audiences.

Without the last two signals, visitors in the EEA are left out of the audiences that Google Ads uses. This is set out on Google's help page on consent settings in GA4.

Consent Mode does not collect consent

Consent Mode does not show a banner. Consent is collected by a cookie banner tool, and Consent Mode passes the answer on to Google's tags. The tool therefore needs to support Consent Mode and be connected correctly in Tag Manager or in your website's code.

Basic and advanced mode

Consent Mode can be set up in two ways. The difference is what happens before the visitor has answered and when the visitor declines.

What happens	Basic mode	Advanced mode
Before the visitor has answered	Google's tags do not load.	The tags load with denied as the default.
When the visitor declines	Nothing is sent to Google.	Cookieless pings are sent to Google.
When the visitor accepts	The tags load and measure as usual.	The tags set cookies and measure as usual.
Modelled conversions in Google Ads	Based on a general model.	Based on a model for your own account.
Modelled visits in GA4	Not available.	Available when traffic is large enough.

The table is based on Google's description of Consent Mode. According to Google, the cookieless pings contain, among other things, a timestamp, details about the browser, the page the visitor came from and which consent applies. As with any request over the internet, the visitor's IP address also reaches Google's servers.

Why we use basic mode

Advanced mode gives better estimates, and that is why Google promotes it. At the same time, the visitor's browser sends information to Google even when the visitor has said no.

In its guidelines on the ePrivacy Directive from October 2024, the EDPB writes that the consent requirement can apply even without cookies. One example is when code on a page makes the browser send information to someone else. The guidelines do not mention Consent Mode by name. My reading is still that the pings in advanced mode fall within what the guidelines describe.

Under Google's policy, you are responsible for making sure consent is valid. The gain from advanced mode is better estimates, and the risk is breaking the consent rules. My assessment is that the gain does not outweigh the risk, which is why we use basic mode.

What disappears from your data

With basic mode, you only see the visitors who have said yes. The rest are missing in several places at once.

• Visits and events in GA4. Anyone who declines does not appear in the reports. That includes where the visit came from and which campaign brought them.
• Conversions in Google Ads. A purchase or enquiry from someone who declined is not recorded. Google can estimate some of them and then adds them to the conversions column.
• Remarketing audiences. Visitors who decline never enter the lists, so the lists grow more slowly.
• The data behind bidding. Automated bidding learns from conversions. Fewer recorded conversions give the system less to learn from.

The estimates also have limits. Google Ads requires at least 700 ad clicks over seven days per country and domain, according to Google's help page on modelling. Modelled visits in GA4 require advanced mode and a certain amount of traffic. According to Google's description of behavioural modelling, you need, among other things, at least 1 000 events a day from visitors who have declined. A smaller account does not always reach those thresholds and then gets no estimates at all.

How to work out what is missing

How many visitors decline depends partly on how the banner looks and who your visitors are. You do not need to guess. Compare GA4 with a source that counts every purchase or enquiry.

1. Get the number of purchases or enquiries for last month from your checkout, your CRM or your inbox.
2. Get the same figure from GA4 for the same month.
3. Divide the GA4 figure by the real figure. An example: if GA4 finds 70 of 100 purchases, 30% is missing from your analytics.
4. Repeat the comparison every month and after every change to your cookie banner.

The numbers will never match exactly, because some purchases are missing for other reasons. A browser extension can block the tags, for example. The comparison still gives you a good picture of how much is missing.

Also check that the signals are arriving. In GA4 you find this under Admin and Consent settings. There you can see whether GA4 is receiving the signals for advertising and analytics.

Read your numbers with consent in mind

Once you know how much is missing, you can read the reports correctly. A campaign that looks expensive per purchase in GA4 may be cheaper in reality. If you change your cookie banner, the numbers can jump without anything having changed in the business.

It also affects your choice of bid strategy. In the post on bid strategies in Google Ads I go through which strategies need many conversions. The same applies to visits from AI services. The guide to tracking AI traffic in Google Analytics 4 only shows the visitors who have said yes.

Your next step

We review your cookie banner and check that Consent Mode sends the right signals to GA4 and Google Ads. We also work out how large a share of your purchases or enquiries is missing from your analytics, so you know how to read the numbers. It is part of our work with measurement and dashboards.

Do you know how large a share of your purchases or enquiries is missing from GA4?