I'm lost in understanding the 28-day window for core web vitals.

  • When did the 28-day collection period start for CWV?

  • Then, if a site has fluctuations on a metric between the 28-day window. For example, LCP day 28 - 2sec then day 24 - 4secs. then day 10 - 1 sec. Means the window will start again?

  • Is it possible to activate a new cycle for the 28-day? And how?

  • How we can calculate the improvements of the new 28-day cycle? Like a table breakdown per day?

  • 1
    Due to its format, this site is limited to just a single question, however you have several here and keep adding more... Therefore this was rolled back to when it was answered. If you have additional questions, please ask them separately - if you like you can reference this question in them.
    – dan
    May 17, 2022 at 16:59

1 Answer 1


All CWV stats from the Chrome UX Report are aggregated over 28 days (as seen in Search Console, PSI, CrUX BigQuery, CrUX API, etc). Some datasets are reported monthly, like the released published on BigQuery. These are 28-day windows into the last calendar month. The other datasets are trailing 28-day windows, which means that you're always looking at data for the most recent 28 days. These datasets change automatically with each daily update.

The aggregations include all user experiences from eligible Chrome users. Experiences on one day may be faster than those on a different day. These all get grouped together in the overall 28-day aggregation, so small fluctuations like that will even out.

This is unlike what you may be used to looking at with site analytics, where the data is aggregated at the daily level. The smallest—and only—granularity of time in the CrUX dataset is the 28-day window.

  • On the URL below, under Validate fixes > mention > Click Start Tracking to start a 28-day monitoring session to check for instances of this issue on your site. So if we don't validate the fixes, the cycle will not start? Page speed insights will not track the new changes? the same values will prevail until this validation pass? support.google.com/webmasters/answer/9205520?hl=en
    – jcdsr
    May 17, 2022 at 10:11

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