First Visit — definition, calculation, and pitfalls

What is First Visit?

First Visit is the very first recorded session from a browser/device to your site or app. It marks the moment a visitor becomes identifiable to your analytics tool (via a persistent identifier like a first-party cookie). From that point on, all subsequent sessions from the same browser/device are return visits.

How is First Visit calculated?

Most tools create a client identifier on the first hit of the first session. If no prior identifier is found, that session is flagged as first. Privacy features, cookie consent, or deletion can cause re-identification and multiple “firsts” for the same human across time or devices.

Typical signals

New client ID in storage (cookie, localStorage, app instance).
First event within a valid session, often tied to an engaged threshold (see Engaged Sessions).

Tool notes

GA4: derives from first_visit (web) or first_open (app).
Alternatives like Plausible, Matomo, and Simple Analytics use similar logic based on first-time identifiers.

Why it matters

Audience growth: pairs naturally with Active Users to track acquisition.
Attribution sanity check: spikes in “firsts” should correlate with campaigns (UTM, Referral, Direct) and chosen Attribution Model.
Cohorts: cohorting by first-visit date powers retention and LTV models (Cohort, Cohort Analysis, LTV).

Edge cases & pitfalls

Consent & blockers: if no storage is allowed, “first” may undercount; if storage returns intermittently, it may overcount.
Cross-domain/app: without proper Cross-Domain Tracking or app↔web linking, one person may register multiple first visits.
Cookie churn: frequent cookie clearing yields inflated “firsts” and deflated Pages Per Session.
Server events: when sending hits via Measurement Protocol or pipelines to BigQuery, ensure consistent client IDs to avoid duplicate firsts.
Quality signals: pair with Conversion and Conversion Rate to evaluate acquisition efficiency.

Implementation checklist

Deploy via Tag Management; verify client ID creation on first hit.
Test cross-domain journeys.
Segment by campaign source and compare engagement (Engagement Time) and outcomes (e.g., CPC, CPA, CPM, AOV).