The Core Web Vitals Google Algorithm Update Is Live

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Google Algorithm Update: Page Experience Explained

Published: August 4, 2021
Last Updated: December 2, 2021
Author: Lindsey Nelson


on June 16th, 2021, Google began to roll out a broad core algorithm update called "The Page Experience Update."¹ This update is intended to bring a better experience to users by prioritizing pages that offer a quality page performance — ie fast load times, and a non-shifting, stable page. Google has always had some page experience metrics — mobile-friendliness,² HTTPS-security,³ and intrusive interstitials⁴ — and they have prioritized fast pages since 2010,⁵ but with the 2021 Page Experience update, they are now introducing three new metrics to measure both speed and overall page experience. These new metrics are called Core Web Vitals.


What are the Core Web Vitals?

The new Core Web Vitals include largest contentful paint (LCP), first input delay (FID), and cumulative layout shift (CLS). In addition to serving as lightweight ranking signals, these new metrics will help website owners monitor and improve the loading speed, responsiveness, and stability of their websites to ultimately build a better user experience (UX). 

core web vitals metrics LCP FID and CLS

Overview of the Three Core Web Vitals 

Largest Contentful Paint (LCP):

LCP: The first metric, largest contentful paint, measures how a user perceives the initial load of a page — it measures the visual part of the load time. More specifically, LCP measures the time it takes for the largest block of visual content on a page to load. 

Largest content element and other elements on a web page

First Input Delay (FID)

Next, we have the first input delay metric. This measures how fast it takes for a page to become responsive. If you’ve ever tried to click something on a web page (like a button) and it takes a sec to respond, that means it has a slower FID. 

vector image phone and button loading first input delay

Cumulative Layout Shift (CLS)

The final metric in the Core Web Vitals is cumulative layout shift. This metric measures page stability. For example, if you’ve ever been trying to read an article, and the page shifts and you have to find your place in the article again, that annoying shift was a page layout shift. The cumulative layout shift is the overall shift in a page's layout as it loads. 

vector phone image of cumulative layout shift

The cumulative layout shift metric has changed⁶ since the Core Web Vitals were first announced back in May 2020. Google has a complicated process for calculating the best way to measure CLS, and their initial research was based on a large-scale analysis of several websites. Even so, when webmasters and developers began to make adjustments to improve their CLS scores, the positive changes they were making were either negatively impacting in some cases. Google adjusted the CLS metric to account for this problem by changing the way they collect the data to determine the CLS measurement.


From an SEO standpoint, there is an incentive to optimize your website for good Core Web Vitals scores because they will become a lightweight ranking factor. Additionally, a good user experience improves bounce rates, conversion rates, and ultimately, revenue, across all marketing channels. Users typically decide whether or not they want to stay on your website within the first 10-15 seconds of arriving, and if your site performance isn't up-to-speed then users will be more likely to navigate elsewhere.

Improving page experience should be about bringing up the overall quality of your web page. So, this means you don’t want to abandon quality content creation efforts or other UX practices in the process of optimizing for this update. As Google’s Martin Splitt said:

“Is it ‘the’ ranking factor (whatever that’s supposed to mean)? No. A fast website with terrible content is likely not what searchers seek… But if you have two good pieces of content and one is going to be frustratingly slow, we might wanna give the faster one a better position, no?”

— Martin Splitt
Martin Splitt of Google comment on core web vitals

We've run over 10,000 Google speed tests on a variety of websites, and most sites score below 50/100 on Google Lighthouse. Part of the reason Google is emphasizing the importance of Page Experience is that most sites need to improve. As more people begin to bring up their page speed, users will see an overall improvement in their web surfing experience. Additionally, the search engine results pages (SERPs) will likely be more competitive in terms of site performance.


Core Web Vitals scores are calculated based on field data from the Chrome User Experience report. With that said, there is additional worthwhile lab data to reference on the journey to improving Largest Contentful Paint, First Input Delay, and Cumulative Layout Shift scores. We will look at both data in this section, as well as Google tools and reports you can easily access and use to measure, monitor, and fix these scores on your website.


One of the key points about Core Web Vitals is that they are based on field metrics or real user metrics (RUM). Google uses anonymous data from Chrome users for feedback, which informs the Chrome User Experience report (crUX). This data is shown in both the Pagespeed Insights tool and the Core Web Vitals report in Search Console.

The Chrome User Experience report is based on page views. This means your most popular pages will have a large influence on your data. This also explains why there may be a notification of insufficient data shown in the PageSpeed Insights report for certain websites, particularly ones with low traffic.

Also, field data that populates in the Core Web Vitals report is slow to update after changes are made because they are based on the last 28 days of data in the Chrome User Experience Report, and more specifically, the 75th percentile of those scores for the more accurate reflection of site performance.


Lab data comes from tools, like Google Lighthouse, that load pages in a simulated environment on controlled network settings and devices without user input. This means it isn’t always reflective of the user experience. First Input Delay, for example, cannot be measured in this environment. However, this data is still instructive and can give you a good idea as to whether you are on the right track with optimizations. Total Blocking Time, for example, has been recognized by Google as a good lab proxy for First Input Delay.


The PageSpeed Insights tool shows an overall score at the top of the page calculated based on Lighthouse data. Directly below that score, however, is a section on data from the Chrome User Experience Report. This shows scores for each of the three Core Web Vitals, as well as First Contentful Paint. There is also a note stating whether the URL passes the Core Web Vitals assessment based on data from the previous 28 day collection period.

When testing a URL, you may see the alert that “The Chrome User Experience Report does not have sufficient real-world speed data for this page.” This is because Google collects anonymized data for the report and there must be enough page loads to report for sufficient data collection.

  • LCP: A score under 2.5 seconds is considered “good” or passing.
  • FID: a score under 100 milliseconds is considered “good” or passing.
  • CLS: A score under .1 is considered “good” or passing.
page speed insights screen shot


The Core Web Vitals report shows how your pages perform for each of the three metrics based on real-world usage data. URLs are grouped together by performance status (“poor”, “needs improvement”, and “good”) for Largest Contentful Paint, First Input Delay, and Cumulative Layout Shift on mobile and desktop. After reviewing this report, you can make changes to your pages. Once those have been made you can “validate these fixes” in the report. This starts a new 28-day monitoring session. Until then, you will see a “pending” status in your report for the particular fixes. After the 28-day session, you will either see a “passing” or “failing” status. Learn more about this report here.

Google search console core web vitals report


The Page Experience report is a new Google report that shows data on each of the page experience metrics over the previous 90 days, specifically the percentage of URLs on your site that provide a “good” page experience and the number of impressions those URLs have received in organic search results. For a URL to have a “good” page experience, it must pass the Core Web Vitals assessment and there must be no issues associated with mobile usability, security, HTTPS, or advertising experience. Learn more about this report here.

Google search console Page Experience report


Google and industry research⁷ ⁸ indicate that there is a strong correlation between good user experience and conversions. For example:

conversion rates drop 12% every 1s increase in page load time
  • Pages that loaded in 2.4 seconds had a 1.9% conversion rate
  • At 3.3 seconds, conversion rate was 1.5%
  • At 4.2 seconds, conversion rate was less than 1%
  • At 5.7+ seconds, conversion rate was 0.6%

Longer page load times have a severe effect on bounce rates.⁹ For example:

  • If page load time increases from 1 second to 3 seconds, bounce rate increases 32%
  • If page load time increases from 1 second to 6 seconds, bounce rate increases by 106%

For the relationship between first contentful paint and reveue: 

  • On mobile, per session, users who experienced fast rendering times bring 75% more revenue than average and 327% more revenue than slow.
  • On desktop, per session, users who experienced fast rendering times bring 212% more revenue than average and 572% more revenue than slow (ALDO Case Study).¹⁰

Here's a comment from Google on the reason for this page experience update:

“Providing a smooth journey for users is one of the most effective ways to grow online traffic and web-based businesses. We hope the Web Vitals metrics and thresholds will provide publishers, developers and business owners with clear and actionable ways to make their sites part of fast, interruption-free journeys for more users.”


This page experience update will make it even harder for sites with poor user experience to rank highly and get traffic from the search results that matter most to their businesses. As previously mentioned, Google will be adding a badge directly in search results to sites with good user experience, so it will be interesting to see how users respond and whether they will be more likely to bypass or ignore sites without this endorsement altogether.

"We believe that providing information about the quality of a web page's experience can be helpful to users in choosing the search result that they want to visit. On results, the snippet or image preview helps provide topical context for users to know what information a page can provide. Visual indicators on the results are another way to do the same, and we are working on one that identifies pages that have met all of the page experience criteria. We plan to test this soon and if the testing is successful, it will launch in June 2021 and we'll share more details on the progress of this in the coming months."

Google Search Central


It should be noted that improving your Core Web Vitals requires technical chops. If you are not a developer yourself, consider assigning responsibility for these scores to a developer on your team, outsourcing the work to SEO experts, or using software designed to improve these metrics

The first thing you should do is understand the problems specific to your site. Perhaps, for example, your site is scoring well on Cumulative Layout Shift, but you have a lot of room for improvement on First Input Delay and Largest Contentful Paint. Run a quick audit of your site through Page Speed Insights or Lighthouse to see where you stand on all three and what strategies are suggested for improvement, and then dive into the Core Web Vitals report in Search Console to see which specific URLs need to be fixed.

If you are scoring in the “green” on all three metrics and therefore passing the Core Web Vitals assessment, simply continue to monitor these numbers on a weekly basis in the lead-up to the update. Unless you are reliant on software, achieving good page speed is not usually a “set it and forget it” type endeavor. It requires vigilance. 

If you are scoring in the “orange” or “red” on any of the three metrics and therefore failing the Core Web Vitals assessment, dive into the recommended suggestions for improving each score and open up that Core Web Vitals report to identify which URLs need to be fixed. Of course, you could simply use Huckabuy Page Speed software to solve the problem. That said, in future articles, we will detail exactly how to improve Largest Contentful Paint, First Input Delay, and Cumulative Layout Shift scores if you want to approach this problem with developer time and resources.

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A Google algorithm update is a change made to Google’s search engine in order to improve the quality, relevance, and overall user experience of its search results.


A core algorithm update is one that is so significant to the algorithm, that Google is compelled to publicly announce the pending changes, usually well ahead of time to give webmasters sufficient time and opportunity to adjust. The June 2021 “Page Experience” update is an example of a “core” algorithm update.


Google updates its algorithm quite often. Sometimes thousands of times per year. But most of these changes go unnoticed. Typically, when a significant change is made, Google makes a public announcement well ahead of time.


The latest (publicly acknowledged) algorithm update is the “Page Experience” update, which introduced new ranking factors tied to the quality of a site’s user experience (loading speed, responsiveness, and visual stability). The rollout for this update began in mid-June 2021 and is expected to be complete by the end of the summer.


The Google Core Web Vitals update is a core algorithm update that began to roll out on June 16th, 2021. It will introduce three new metrics into the algorithm that measure and help rank sites based on the quality of their user experience. Specifically, they look at how quickly the largest piece of content in the initial viewport loads, how responsive the page is, and how visually stable the page is. The three metrics that make up the Core Web Vitals are called Largest Contentful Paint, First Input Delay, and Cumulative Layout Shift. 


Core Web Vitals are important primarily because they are set to become a new ranking factor in Google’s search algorithm in 2021. They are also important because they measure the quality of a site’s user experience, which is important for all marketing channels and has a big impact on key metrics like bounce rates, conversions rate, and revenue.


In order to pass a Core Web Vitals assessment, your web page must receive a passing score for each of the metrics. For the Largest Contentful Paint, you must be under 2.5 seconds. For First Input Delay, you must be under 100 milliseconds. And for Cumulative Layout Shift, you must be under 0.1.


There are numerous tools and reports that can be used to monitor and measure your website’s Core Web Vitals. We recommend using any of the following: Google’s PageSpeed Insights tool and both the Core Web Vitals and Page Experience reports in Google Search Console. All three of these tools use real-world user data to collect information about the experience your site provides to users over about a 30 day period. In order to troubleshoot fixes to your website for Core Web Vitals, we recommend using Google Lighthouse. This tool gives you an estimate of how your web page will perform for the average user by using a controlled testing environment.



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