Data dropped after the cookie banner: what Consent Mode changes

Published October 10, 2026 by the UTM Builder team at Limner.

If the banner blocks Google tags until the person clicks, anyone who declines sends nothing to GA4 or Google Ads, and the drop shows up in your reports. In advanced consent mode, a decline still generates cookieless pings, which Google uses to estimate part of what’s missing. Choosing between the two is a technical decision and a legal one.

Basic or advanced

Google Ads help describes the two ways to implement it:

	Basic	Advanced
Google tags	blocked until the user interacts with the banner	load with defaults set to denied, unless configured otherwise
When the person declines	nothing is sent, not even the consent status	consent state and cookieless pings are sent
When the person accepts	tags load and work normally	cookies are written and all measurement data is sent
Conversion modeling in Google Ads	general model	advertiser-specific model

What happens in GA4

People who decline analytics_storage don’t get a persistent identifier. The behavioral modeling help gives an example: ten page views without an identifier could come from ten people or from just one. Modeling estimates that behavior from the people who consented, but the property has to qualify:

advanced consent mode on every page;
at least 1,000 events per day with analytics_storage='denied' for at least 7 days;
at least 1,000 users per day with analytics_storage='granted' on at least 7 of the last 28 days.

Meeting these doesn’t guarantee that the property qualifies, and without enough consented traffic the events from people who declined aren’t reported. When modeling is active, the estimated data shows up under the Blended reporting identity, in Admin, Data display, Reporting identity.

What happens in Google Ads

Google uses the cookieless pings in conversion modeling, as long as the tags reach a data collection threshold. According to the help, after at least 7 full days of implementation Google Ads and GA4 have enough data to show the uplift, and the number only appears once the segment passes the minimum threshold. If you didn’t have consent mode before, you may even see conversions go up.

The help lists the tags with built-in consent checks: Google tag, Google Analytics, Google Ads, Floodlight and Conversion Linker. For everything else, such as other platforms’ pixels in Tag Manager, the advice is to add the check in the tag’s configuration, under Advanced Settings, Consent Settings.

If it dropped more than it should have

Google’s consent mode troubleshooting page says to start with Tag Assistant, in the Consent tab:

Empty tab: consent mode isn’t on the page, or the Google tag is blocked.
No default set: set at least ad_storage, analytics_storage, ad_user_data and ad_personalization.
Default set too late: the default command has to run before any tag reads consent and before commands such as config and event.
Consent doesn’t update: the banner has to send the update command when the person clicks.
Region: region-specific defaults use ISO 3166-2 codes, and the most specific one takes precedence.

gtag('consent', 'default', {ad_storage: 'denied', ad_user_data: 'denied', ad_personalization: 'denied', analytics_storage: 'denied', wait_for_update: 500});

wait_for_update, in milliseconds, gives a banner that loads later time to call update before the tags send data.

EEA, UK, Switzerland and Brazil

The requirement Google documents is tied to the European Economic Area. Tag Manager help says that to keep using tags for measurement, ad personalization and remarketing, you need to collect consent from end users in the EEA and send those signals to Google, with the ad_user_data and ad_personalization parameters. The EU user consent policy applies to users in the EEA, the UK and Switzerland. The Google pages we checked don’t mention Brazil or the LGPD.

In Brazil, the reference is the LGPD, Brazil’s general data protection law. The ANPD, the national data protection authority, published its guidance on cookies and personal data protection in October 2022. It says legitimate interest will rarely be the most appropriate legal basis when cookie data is used for advertising, and that consent may be considered more appropriate in that case. Among good practices for banners, it lists a button to reject all non-essential cookies, and consent-based cookies turned off by default. The same guidance analyzes an example of audience measurement cookies based on legitimate interest, in a case with aggregated data and no sharing with third parties.

This guide isn’t legal advice. The legal basis, the banner copy and the choice between basic and advanced are decisions for your legal team or data protection officer. The media team’s job is to make sure the implementation does what was decided and to explain to the client why the numbers changed.