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).


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.


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.


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

The cumulative layout shift metric has changed⁶ since the Core Web Vitals were first announced 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 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. Users will be more likely to navigate elsewhere.

Improving page experience should be about increasing your overall webpage quality. 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

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, and also discuss 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 if 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 which is the result of a calculation based on Lighthouse data. Directly below that score 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.

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 are able to make page updates. Once those edits 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.


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.


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

  • 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.”"

- Google

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 business. As previously mentioned, Google will be adding a badge directly in search results to sites with good user experience. It will be interesting to see how users respond and whether they will be more likely to bypass or ignore sites without this endorsement.

"We believe that providing information about the quality of a web pages 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 will 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. Now you can 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.