Google Core Web Vitals Update – What is means for your website

by Anthony Godley

In May 2021, Google will be implementing its Core Web Vitals update to their algorithm. For the first time Core Web Vitals data will have a direct impact on Ranking Signals. In this article we will discuss what we know and what you need to consider for your website.

The complete algorithm update is a combination of several page experience signals and Core Web Vitals signals, as categorised below:

  • Speed UX (User Experience)
  • Website Responsiveness / Mobile Performance
  • Page Visual Stability
  • Safe Browsing / HTTPS Security
  • Intrusive Interstitial
  • Largest Contentful Paint 
  • First Input Delay 
  • Cumulative Layout Shift

Through this article we will look at what each one of these signals means, and what considerations need to be taken to ensure your website does not lose ranks.

It is important to recognise that while these Core Web Vitals updates are going to become important rank signals, they are still only part of the broader SEO ranking landscape which are currently is made up of 200 individual ranking signals, which can be VIEWED HERE. Before we deep dive into the specifics of the algorithm updates, we have outlined the fundamental metrics that make up the Core Web Vitals data:

Core Web Vitals Data

Largest Contentful Paint (LCP): What the LCP data shows is the real time load speed of the point of view for the user. When a user opens your web page, the time taken for the content to load from the first point of contact is the LCP. LCP is the measurement of loading performance.

First Input Delay (FID): The FID is the time taken from the original LCP to the point of user interaction with your website. The interaction type could be anything from clicking a button, opening a menu, or submitting a form. The FID is a measurement of interactivity.

Cumulative Layout Shift (CLS): The CLS is a metric that measures how quickly a page becomes stable. For example, if a user loads your web page, then clicks a button, but just prior to clicking a button the page shifts then the page will be considered unstable. CLS is the measurement of stability.

Speed UX (User Experience)

The Core Web Vitals data metrics are a series of factors that Google considers important across the entire web page experience. Website speed and performance are a major part of that experience as Google requires websites to quickly deliver content that users have requested to see.

Within the overall speed and performance indicators we see the various factors which consist of the Largest Contentful Paint, First Input Delay and Cumulative Layout Shift metrics as detailed above.

The speed of a website which is often referred to as load speed will become a significant ranking signal after the Core Web Vitals update is fully implemented.

There are a wide range of different factors that can affect website speed and performance. Some of the most common are detailed below:

  • Heavy images and video content can significantly slow the loading speed of a website. It is always good practice to compress image and video files, and use compression plugins and tools on your website
  • Poor hosting usually means poor speed. Upgrading to higher quality hosting will give your website better performance and rank signals
  • Lazy loading is a technique that ensures that images are only loaded should a user require them or scroll through to them. This means a website can load much quicker as only the parts of the website the user is viewing need to load
  • Removing large elements such as bloated CSS/JavaScript, which is typically found when website are built using templates in WordPress, Magento, Shopify etc, will improve speed as browsers will not need to load so much code. Excessive DOM and poor caching protocols can also increase load times and contribute to the overall Largest Contentful Paint performance score

There are many speed and performance factors that need to be consider ensuring a fast and efficient website.

The following tools will help you understand how your website is performing and what steps need to be taken to improve the website speed:

Website Responsiveness / Mobile Performance

While website performance on mobile devices and across the wide range of screen sizes and browsers has long been a signal for trust and rank, the release of the Core Web Vitals update will increase the rank signal value of mobile and device performance.

It was back in 2016 that AMP (Accelerated Mobile Pages) were officially integrated into Google mobile search results. AMP will now play an even more important role in rank signals.

Below are six fundamental considerations to improving mobile performance and ensuring your website responds positively from the Core Web Vitals update.

  • Use Accelerated Mobile Pages
  • Implement Schema Markup
  • Ensure Responsive HTML is Used
  • Compress Images & Video
  • Remove Flash
  • Use Content Accordions

These mobile performance indicators are not new. In fact they have been valuable since Mobilegeddon in 2015, however in a post Core Web Vitals landscape, these signals will become more valuable than ever before.

Page Visual Stability

The Visual Stability of a page forms part of the Core Web Vitals Metric Cumulative Layout Shift and will become part of a major rank signal through May 2021.

The Page Visual Stability can be defined as the shifting of web page elements during the loading of the web page.

There are several reasons why Cumulative Layout Shift occurs which we discuss further in the CLS section.

The First Input Delay, which is also a Core Web Vitals metric, can measure the responsiveness of a web pages visual stability, and quantifies the experience the user is experiencing when making that first interaction with the web page. The Cumulative Layout Shift then measures that stability and quantify the amount of element shift within the visible page content; these measurements produce a score, and the higher the score the more positive the rank signal


Bryan McQuade, a Senior Software Engineer from Google who has worked on the Core Web Vitals update, explains how Visual Stability effects the Core Web Vitals rank signals.

Safe Browsing / HTTPS Security

HTTPS or secure web browsing is again not a new rank signal. However, from May 2021 onwards, those sites that are not secure with HTTPs web browsing are going to get penalized much heavier and those sites that are HTTPs secure, will produce more positive rank signals.

If your website is not HTTPs secure, simple install an SSL which can be done through your hosting environment.

Intrusive Interstitial

Intrusive Interstitial was first discussed by Google just before the Mobilegeddon updates in 2015. So, again nothing completely new with the fundamentals of what Intrusive Interstitial is.

However, similarly to HTTPs security, the implications of Intrusive Interstitial will change, with websites that do not conform to the guidelines losing credibility and rank signals.

In simplistic terms, Intrusive Interstitial are pop-ups that appear when you land on a web page. Pop-ups and ads usually cover significant parts of the web page content itself and are considered bad experience if it does not follow the guidelines set by Google below:

  • Ensure the interstitial does not cover most or all the web page content
  • Ensure the interstitial is responsive and has clear ways to close on mobile
  • Ensure the interstitial shows on request such as being triggered by an action and does not pop up without being prompted


Below are the new major rank signals that will come into effect as part of the Core Web Vitals update through May 2021

Largest Contentful Paint (LCP)

In its most basic terms, the Latest Contentful Paint is simply, how fast a web page loads. The concept is easy, but in practice there are a wide variety of considerations. LCP is highly influenced by page rendering time, image sizes, video weight and viewport text (which is essentially the area of a web page a user can see at anyone time).

This is what Google will now be looking at very closely. For every step in the user journey, what is visible in the viewport, what is the largest image, the largest block of text, largest video and how long does it take those pieces of content to load.

These response times will be influenced by the quality of the server that your website is hosted on, the quality of the CSS & JavaScript.

Cumulative Layout Shift (CLS)

What Google will be looking for, is how quickly the web page being loaded becomes perfectly stable. When you open a web page, it is relatively common to see elements shift about as the web page loads. You may have even had an experience where an element seemed to be loaded, but when you clicked on it, it suddenly jolted slightly meaning you either missed the clicked or clicked on the wrong button.

Although quite common, this is poor experience and Google will be penalizing websites where this layout shift occurs.

The most common reason for layout shifts are non-defined image sizes which means that the image size itself has not been defined within the HTML. If you have an image which is 800px X 400 px, this needs to be properly defined with the HTML code.

Animations are another common cause of layout shift.

Google will be measuring the time a web page becomes stable with those pages that stabilize completely within 2.5 seconds producing favorable rank signals.

First Input Delay (FID)

The First Input Delay measures how quickly a user interacts with an element on the web page. For example, a user clicks on your web page and the page content opens, but how quickly did that user click on a button, scroll to a piece of content, or complete a form; how quickly did the web page content attract a user to an action.

The purpose of any web page is to provide the user with a valuable experience, to get the user to do something and to interact with the user. A web page that offers nothing, where users get nothing from it or have no reason to interact is considered poor experience.

When creating web page content and UX wireframes, consider why the user would like to see this content, as well as what content they would like to see. Consider how the content should be presented and consider what interaction or conversion elements need to be included to engage the user or improve the chances of the user making your preferred action.


So, this is the Core Web Vitals update which will be affecting all websites through and beyond May 2021.

If your website is not currently set up to view the Core Web Vitals data, set up a Google Console Account, and submit your XML sitemap, and the latest insights will be available.

For a deeper view of Core Web Vital performance, run an audit in the performance tools we listed in earlier in this guide.

If you want your website to not only pass the Core Web Vitals assessment, but aggressively capture organic market share and ranks, Contact Our SEO Specialists for a free, transparent quote on what needs to be done.

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