Days since last session dimension
The days since last session dimension reports how many days have elapsed since the user's previous session. GA4 computes it from the stored last-session timestamp on the current identity. It supports recency and re-engagement analysis, but it can only be calculated when GA4 still recognises the user — if the identifier was cleared, the prior session is invisible and the return is counted as new, so the gap is undercounted.
What this means
Days since last session expresses recency: the number of whole days between the current session and the user's last recorded session for the same identity. GA4 derives it by comparing the current session's timestamp with the stored previous-session time.
It complements session number — one tells you how many visits, the other how long between them — for cohort and re-engagement reporting.
Why identity loss distorts it
The dimension needs a remembered previous session. When the client identifier is cleared or consent denied, GA4 has no prior session to compare against, so the visit is treated as new and no gap is reported. This systematically undercounts true return rates and overstates first-time visits. Read recency together with consent and identity context.
- Day-gap to the previous recognised session
- Requires GA4 to still recognise the user
- Identity loss makes returns look like first visits
How it appears in analytics and logs
A value is the day-gap to the previous recognised session. It exists only when GA4 still has the user's prior session; otherwise the visit looks like a first session.
Diagnostic use case
Use days since last session to study recency — how quickly users return — and to segment dormant versus frequently returning visitors.
What WebmasterID can help detect
WebmasterID can frame recency from first-party signals while being explicit that cleared identity removes the previous session GA4 would have compared against.
Common mistakes
- Assuming the gap is exact when identity may have reset.
- Treating absent gaps as genuine first-time visits.
- Ignoring consent effects on recency reporting.
Privacy and accuracy notes
The gap is computed from a first-party last-session timestamp on the device identity, not cross-site history. Identity resets legitimately erase the prior reference point.
Related pages
- GA session number dimension
The GA session number dimension records the ordinal of the current session for a user — 1 for their first ever session, 2 for the second, and so on. GA4 derives it from the ga_session_number event parameter, incremented per device/client identity. It is the basis for engagement-by-visit analysis, but it resets whenever the underlying identifier is cleared, so consent and cookie loss inflate the count of session number 1.
- New vs established user dimension
The new vs established user dimension classifies a user as 'new' or 'established' based on whether GA4 had recorded prior activity for them before the reporting window. It is user-scoped and derived from the user's first-seen timestamp. This differs from the session-scoped new-vs-returning split, which classifies each visit; conflating the two produces mismatched user and session counts.
- Cohort dimension
The cohort dimension groups users by a shared starting point — typically their acquisition date — so you can follow each group's behaviour across subsequent days, weeks, or months. GA4 builds cohorts in the Cohort exploration from a first-touch criterion and a return criterion. It is the backbone of retention analysis, but small cohorts and identity loss can make later-period values unstable, so trends matter more than single cells.
- Privacy-first analytics
Recency analysis without cross-site identity.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.