Cumulative Layout Shift (CLS) Update Planned for May 2021

Every year Google releases lots of algorithm changes 99.9% of them you will not even notice, but when a big one is planned they tell you in advance to allow for website owners to prepare for them. In May 2021 there is a big update planned which is primarily based around CLA or Cumulative Layout Shift and will be a core ranking factor for websites the world over.

As it is soon to become a ranking factor you need to know what it is, how it is going to affect your website and how to optimize for it.

google update cumulative layout shift

What is Cumulative Layout Shift?

CLS is the unexpected movement of items on a website while the page is still downloading. This can be anything from fonts, images, videos, buttons or anything that the viewer can see on the page/blog post. If you have ever visited a website and been reading some content or went to click an item within that page and it suddenly moved that is a layout shift. A score is given by Google to a website with a total of all these movements combined and is called the cumulative layout shift.

Google is adding this as a score within core web vitals and as a ranking factor as ultimately a poor CLS score impacts user experience, it is also used by spam websites and or fraudsters as a means to get users to click ads or sign up for services on less than reputable websites. User experience is a broad term but it is probably one of the biggest changes to how websites work, how search engines score your website and ultimately how users view your website, hence Google adding more weight to it over the last few big updates.

Why does Cumulative Layout Shift matter?

There are various ways your website can frustrate or excite your users, and CLS is a measurement that may highlight some of the negative experiences. Things like reading content and it moving down the screen as an advert changes shape further up the screen can lead to users being frustrated and clicking away from the content, or even in extreme cases when it comes to CLA in eCommerce, used to defraud people into buying a larger quantity of goods than they had expected. 

What’s a Good CLS Score?

A cumulative shift score can be as low as 0 for fully static pages and gets higher the more layout shifts occur on the page. Google recommends that you keep your CLS score under 0.1, and scores sites as follows:

  • Good – CLS below 0.1
  • Needs improvement – CLS between 0.1 and 0.25
  • Poor – CLS above 0.25
google update cumulative layout shift

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Does Your CLS Score Affect Your SEO?

Yes is the simple answer and it is being made a ranking factor, just how much it will impact the SEO on your website is not yet clear, some think it will be a large ranking factor others think it will be minor. The truth is no one will truly know until it is rolled out but it is advised to be prepared for it as some reports suggest that it could be as much as 5% of the overall ranking score given by Google, which may not seem like a great deal but it could make the difference between ranking in a keyword niche and not ranking at all.

How to Reduce Cumulative Layout Shift

The most common causes of poor layout shift are:

  • Unspecified image sizes 
  • Ads, embeds, and iframes without dimensions
  • Dynamically injected content
  • Web Fonts

There is also one big factor when it comes to CLS and WordPress that many might not consider and that is content that is moving such as sliders, or content that moves in from the side of the page.

To use an example of this would be to use customer testimonial sliders as an example, you want to showcase these and it is a good marketing method, but so many put them in a slider and fail to see that every review is a different length, meaning that the slider gets bigger and smaller as it slides along. To combat this within WordPress adding it to its own section and defining the measurements into a fixed box is a way to stop the rest of the page and your CLS score from being impacted.

Adding image dimensions and ensuring that your fancy fonts do not suddenly kick in causing all the content to move are also good ways to reduce your layout shift. The irony of this is that probably one of the biggest culprits involved in this is Google themselves. People love Google fonts, and yet they are part of the problem as they load a lot slower than most fonts and add to the CLS issue! Google ads also compound the layout shift issue.

Websites with a heavy ad presence will suffer from high layout shift scores if they have not been designed correctly. Dynamic ads tend to change in shape and size a lot, meaning they cause issues with the rest of the web page moving when they do change, you can of course combat this by reducing ads high up on the page and also setting the min-height value to a wrapper around each of your ad units.


Prepare For Cumulative Layout Shift

Like most things when it comes to websites and SEO its lots of smaller things that come together to build the overall experience and functionality, and the best way to combat them is to prepare and test. Try changing one aspect of your website that might be causing layout shift, then test the results, then move onto the next thing and test the results and so on and so forth.

There is no short cuts or magic button to solve layout shift in one go sadly, so having someone check over your site who knows what to look for it probably the easiest option to get ready for the big update rolling out in May.

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