Cookie consent is the permission a site asks for before setting cookies, or using similar storage, that are not strictly necessary to provide the service. In the EU and UK this requirement comes mainly from ePrivacy rules, with the GDPR defining what valid consent looks like. Sites usually collect it with a banner from a consent management platform (CMP), which records choices and tells tags what they may do.
Valid consent, in plain terms
European guidance generally expects consent to be freely given, specific, informed and unambiguous, and as easy to withdraw as to give. Practically, that has meant banners with a clear way to reject, no pre-ticked boxes, and no non-essential tags firing before a choice. Rules differ by country and change over time, and this is not legal advice: confirm requirements with counsel.
What it does to analytics
Visitors who decline will not be measured in the usual way. Expect lower session and user counts after launching a banner, and a shift in channel mix because consent rates differ by source and device. Annotate the launch date.
- Lower recorded traffic in regions where the banner applies
- Gaps in attribution for users who decline
- Modeled data in GA4 if advanced Consent Mode is used and the property qualifies
Implementation checklist
Classify every cookie and tag on the site, block non-essential tags until consent, connect the CMP to Consent Mode or your tag manager, and test that declining actually stops the tags. Google has required publishers and advertisers using some of its products with EEA and UK traffic to use a CMP certified by Google, so check whether that applies to you.
Example
Explaining a post-banner drop
Imagine Saffronvale, an HR analytics tool, adds a compliant banner across Europe. Recorded EU sessions fall while sign-ups in its own database stay level. The team annotates the change, reports trial sign-ups from the product database for that region, and stops treating GA4 session counts there as a complete total.
Common mistakes
A banner that changes nothing
If tags fire regardless of the choice, the banner is decoration and a compliance risk.
Comparing pre- and post-banner traffic without a caveat
The drop is mostly measurement, not demand.
Questions
In many EU and UK contexts, yes, unless a specific exemption applies. Some regulators have published narrower exemptions for certain audience measurement. Check the current guidance for each country you serve.
