How Consent Mode v2 affects your GA4 data (and how to recover it)

If part of your traffic rejects cookies — and in Europe it's usually the majority — your Google Analytics 4 reports stop counting those people. The good news: Consent Mode v2 lets you recover a large share of that data through modeling. Let's see exactly what's lost, how it's rebuilt, and what you need to do to avoid flying blind.

What you lose when someone rejects

Without analytics_storage consent, GA4 can't write its client cookie (_ga). Without that cookie, three things happen:

It doesn't recognize returning sessions: the same user coming back tomorrow is counted as new, so your user and retention metrics inflate or break.
Attribution is lost: GA4 can't link the conversion to the campaign that drove it.
Reports turn off: demographics, interests and certain audiences stop populating for that traffic.

Around 50% of the data is estimated to be lost to cookie rejection in European traffic. And since July 21, 2025, Google applies automated enforcement of Consent Mode v2: if your site doesn't send valid signals, tracking, remarketing and reports are silently disabled for EEA/UK traffic, with no warning or grace period.

Behavioral modeling vs. conversion modeling

GA4 uses two types of modeling, and it's worth not confusing them:

Behavioral modeling: estimates users and sessions for those who rejected, based on the behavior of those who accepted in similar contexts. It fills the general reports.
Conversion modeling: specifically estimates the conversions and key events that couldn't be observed.

Both are fed by the cookieless pings sent even after rejection. Together they can recover up to 70% of lost attribution without identifying anyone individually: the model works with aggregates, never with specific people.

Requirements to enable modeling

Modeling doesn't turn on by itself: your property must clear minimum volume thresholds for the estimates to be reliable. Broadly, GA4 needs:

Requirement	Approximate threshold
Daily events with `analytics_storage='denied'`	≥ 1,000 for 7 days
Daily users with `analytics_storage='granted'`	≥ 1,000, 7 of the last 28 days
Consent Mode setup	Advanced (basic sends no pings)

Practical implication: a small site may not reach those thresholds and so won't receive modeled data. In that case you'll see the gaps as-is — one more reason to enable advanced mode early and build up history.

Basic vs. advanced: the decision that matters most

Basic mode: Google tags are blocked until the user accepts. Whoever rejects generates no signal → zero modeling and zero data from that visitor.
Advanced mode: tags load with a denied state and send cookieless pings → this enables modeling and recovers much of the data.

For most sites that rely on analytics, advanced mode is the right choice: it's privacy-compliant and still doesn't leave you blind.

How to read your reports afterwards

When modeling is active, GA4 blends observed and modeled data in the same reports. Keep that in mind when analyzing:

User and conversion figures include an estimated portion; don't treat them as an exact count to the decimal.
Compare trends and proportions rather than absolute day-to-day values.
If you see an odd jump after a date, first check that consent is being sent correctly before blaming the business.

What to do today

Implement Consent Mode v2 in advanced mode.
Verify that analytics_storage travels correctly (check the gcs parameter — we explain it in this guide).
Ensure the minimum event volume to be eligible for modeling.
Document for your team which part of the reports is measured and which is modeled.

Conma configures advanced mode for you and guarantees the signals arrive in the right order, so GA4 is eligible for modeling from day one.