Nth week dimension
Nth week is the dimension that numbers weeks by their offset from the start of the selected range — week 0, week 1, and so on. It is the weekly analog of nth day, built for multi-week retention curves and cohort decay where you want week-1 retention to align across cohorts regardless of when each began. Its numbering is relative to the report's range and resets when the range changes.
What this means
Nth week indexes weeks from the start of the chosen range, so multiple cohorts each run week 0, week 1, and onward. Overlaying them aligns equivalent retention positions, which is exactly what retention and decay analysis needs.
It trades nth day's granularity for steadier, less noisy weekly buckets.
When to choose it
Prefer nth week over nth day when daily fluctuation obscures the underlying retention shape, or when your product's natural cycle is weekly. As with nth day, the numbering is range-relative and resets if you change the date range, so it has no absolute calendar meaning.
Pair it with the cohort dimension to define who belongs to each curve.
- Offset in weeks from the range start
- Aligns multi-week cohort retention
- Range-relative numbering, like nth day
How it appears in analytics and logs
An nth week value is a relative week offset, not a calendar week. Like nth day, it is meaningful only within the range that produced it.
Diagnostic use case
Use nth week to align cohorts on their week-one, week-two and later retention, smoothing the daily noise that nth day carries.
What WebmasterID can help detect
WebmasterID can express timing as weeks-since-baseline first-party, supporting retention curves without third-party tracking.
Common mistakes
- Using nth week where the cycle is genuinely daily.
- Reading nth week as a calendar week number.
- Comparing nth-week curves from differently-sized ranges.
Privacy and accuracy notes
Nth week records a relative week index, not identity. WebmasterID can index weeks from a baseline first-party without profiling visitors.
Related pages
- Nth day dimension
Nth day is the dimension that numbers each day by its offset from the start of the selected date range — day 0, day 1, and so on — rather than by calendar date. This relative indexing is what lets you overlay two periods of equal length so their day 1s align, the standard technique for period-over-period and launch-cohort comparison regardless of the actual calendar dates involved.
- Nth month dimension
Nth month is the dimension that numbers months by their offset from the start of the selected range — month 0, month 1, and so on. It is the longest-horizon member of the nth-period family, built for lifecycle and long-term cohort analysis where retention is measured over many months. Its numbering is relative to the report range, and like its siblings it carries no fixed calendar meaning.
- 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.
- Web analytics
Cohort retention curves first-party.
Sources and verification notes
- Google Analytics Help — [GA4] Dimensions, metrics, and other termsDefines nth-week as an offset from the range start.
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.