Google’s Core Web Vitals testing tools take 28 days to gather aggregate field data, and that likely won’t change any time soon.
Google Search Advocate John Mueller stated as much during the Search Central SEO hangout recorded on March 5.
’s IT Director, Vahan Petrosyan, asked Mueller about this while noting the challenges the 28-day window creates for developers and SEOs.
When a change is made to a site to improve Core Web Vitals, it will be at least 28 days before that change is picked up by Google’s testing tools.
It’s unlikely that the 28 day window will ever get smaller, according to Mueller’s response which you can read below.
Google’s John Mueller on Core Web Vitals Data
Mueller doubts the collection of Core Web Vitals data will ever change from the way it is now.
“I don’t know. I doubt it, because the data that we show in Search Console is based on the Chrome User Experience report data which is aggregated over those 28 days. So that’s the primary reason for the delay there. It’s not that Search Console is slow in processing that data or anything like that. It’s just the way that the data is collected and aggregated, it just takes time.”
It’s not Google’s intention to analyze and report Core Web Vitals data in real-time. The scores represent aggregate data, because Google wants to ensure the site consistently provides a good user experience over an extended period.
If SEOs and developers want the data faster, Mueller recommends they conduct their own tests with third party tools or the PageSpeed Insights API.
“So usually what I recommend when people ask about this kind of thing where it’s like, “I want to know early when something breaks,” is to make sure that you run your own tests on your side, kind of in parallel for your important pages. And there are a bunch of third party tools that do that for you automatically.
You can also use the Page Speed Insights API directly and pick, I don’t know, a small sample of your important pages and just test them every day. And that way you can kind of tell if there are any regressions in any of the setups you made fairly quickly.”
Mueller points out that the lab data offered by third party tools is not the same as field data, which is what Google reports on.
“Obviously a lab test is not the same as the field data. So there is a bit of a difference there. But if you see that the data lab test results are stable for a period of time, and then suddenly they go really weird, then that’s a strong indicator that something broke in your layout or in your pages somewhere.”
Mueller acknowledges the way Google collects data makes things harder for people, and measuring cumulative layout shift (CLS) is especially tricky.
If SEOs feel that Google’s calculations aren’t making sense, Mueller encourages them to reach out to the Chrome team directly.
“It makes things harder. It’s not that we’re trying to make things harder it’s just the way that this data is collected in Chrome. It just takes time to be aggregated.
The cumulative layout shift is sometimes, I think, tricky to interpret and figure out what exactly is causing the issues there.
I think for things where you feel that the calculations are being done in a way that doesn’t make much sense, I would also get in touch with the Chrome team. I think especially Annie Sullivan is working on improving the cumulative layout shift side of things. And just make sure that they see these kind of examples.
And if you run across something where you say, “oh it doesn’t make any sense at all,” then make sure that they know about it. It’s not so much that from Google’s search side we would try to dig in and try to figure out what exactly is happening with that score, but we kind of need to rely on the score from the Chrome side.”
Lastly, Mueller reminds SEOs that Google plans on updating the Core Web Vitals roughly once a year.
While cumulative layout shift is a Core Web Vital this year, for example, it may not be one next year if Google determines it’s not vital to providing a good user experience.
“And our goal with the Core Web Vitals and page experience in general is to update them over time. So I think we announced that we wanted to update them maybe once a year and let people know ahead of time what is happening.
So I would expect that to be improved over time. But it’s also important to get your feedback in and make sure that they’re aware of these weird cases.”
Hear the full discussion on Core Web Vitals in the video below:
