Mobile-First Indexing: Google’s March 2021 Update

Mobile-first indexing will be used by Google on all websites as of March 2021. That means, if your website isn’t mobile-optimised, you may see a drop in rankings and traffic, or even be removed altogether.

What is Mobile-First Indexing?

The number of mobile searches has been higher than the number of desktop searches for over 5 years now, and it continues to increase. That means that anyone coming to your website from a search will most likely be presented with a smaller version of your site than is seen on desktop.

For a long time now, it has been an extremely important part of search optimisation to ensure your site looks good and works well on a mobile, but in March this year, Google will make it absolutely vital.

The search engine is updating to a mobile-first algorithm across the board, which means that only content from your mobile site will help you rank.

If your site isn’t already optimised for mobile, now is the time to invest some time and money into doing that.

If you think your site is already mobile-optimised, it’s worth checking that you are fully up-to-date with and following best practices, to avoid any big changes in your rankings and traffic.

What is a Mobile-Optimised Website?

A mobile optimised website is one that looks good and works well on mobile devices, not just on a desktop or a laptop.

If you’ve ever clicked on a website on your mobile and had to zoom in to read tiny text, or had to keep swiping left and right to read it, then that website was not mobile-optimised. The user shouldn’t even really be aware that they’re on a mobile-optimised website: it should be as easy and as natural an experience as on a desktop.

We’ll go into some more detail about how you can optimise your website for mobile below.

Check if You’re on Mobile-First Indexing

Around 70% of sites are already on mobile-first indexing, so you may have already seen changes in your rankings and made adjustments to improve your site for mobile.

To check whether or not you’re already on mobile-first indexing:

  1. Log into Google Search Console.
  2. Click Settings
  3. Under the About section, look at the Indexing Crawler
  4. If it says Googlebot smartphone, you’re already switched.
  5. If not, you may be using a site that’s not well suited to mobile-first indexing, and it’s even more important that you make changes now.

Indexing crawler on Google Search Console

Preparing for Mobile-First Indexing

Although, as of March 2021, you’ll have no choice about using a mobile-optimised website (if you want to rank well, that is!), this is a positive step. Google is making this change because it’s beneficial to the user, the person doing the search. And anything that helps the user is something that helps you effectively reach out to them to offer your products or services.

So what can you do to prepare for the change?

M-dot sites

An m-dot site is a mobile site that shows similar content to your desktop site in a way that is more suited to mobile viewing. It follows the format

These are, in fact, completely separate to your desktop site, can by quite complex, and are now outdated. If you use one of these, then best practice would be to get rid of it entirely and instead focus on optimising your main site so that it is responsive to all devices.

Mobile-First Design

A true mobile-first design means that your site should be responsive to whatever screen it’s being viewed on. Text should resize, image resolution should adjust, and orientations should adapt to give the user the best possible experience, whatever device they use.

You should also consider the different ways people use a mobile compared to a desktop. Do you have something that shows up on desktop when you hover your mouse over it? Hover won’t work on a mobile, so you need to make adjustments. A side menu on a desktop may take up most of the screen on a mobile, so consider using a hamburger menu instead. There are all sorts of small but important adjustments that you can make to a responsive site that will make the experience straightforward and enjoyable for any user.

In Google Search Console, you can head to Enhancements > Mobile Usability to see how mobile-friendly your website design is, and receive suggestions for improvements.

Content Optimisation

If you have a lot of content on your website, you may have elected to cut this down in the mobile version so that users don’t have to scroll through so much text, images and video.

While it can be beneficial – to an extent – to have less content on your mobile site in order to improve user experience, remember that Google will now no longer see any of the content on your desktop site. At all. So you must make sure that your most important content is available on mobile, too.

Instead of removing content from your mobile site altogether, consider making use of design options such as tabbed content where the information isn’t necessarily available in the main body, but, if interested, the user can see more with a simple tap. Once upon a time, Google discounted this ‘hidden’ content, but they no longer do this if the features are used to improve user experience.

You should also ensure that items like headings and meta data are as well-optimised on your mobile site as they are on your desktop site. Ideally, they should be exactly the same.


Google Search Console's Core Web Vitals for MobileSpeed plays a big part in Google’s algorithm, and studies have shown that 53% of mobile users will leave a site if it takes more than three seconds to load. This has always been important to Google, and will become even more so in the update.

You can check your site speed in Google Search Console by logging in then going to Enhancements > Core Web Vitals > Mobile. A chart will show you how your pages are performing and suggest where you can make improvements.

Pop-Ups and Adverts

Pop-ups, when used well, can be a great way of getting users to take a particular action, such as subscribing to your mailing list. On the flip side, they can be incredibly annoying, and in the updated algorithm, especially, they could be detrimental to your rankings. Make sure you don’t have too many, that they’re easy to close, and that they don’t take up too much of the screen.

Similarly, if you have banner ads on your site, consider how they look on mobile. While on desktop they might be a size that’s visible but non-imposing, on mobile they could take up the whole screen and even overlap your own content.


Does your mobile site include the same navigation as your desktop site? If not, Googlebot may find it harder to crawl certain pages. For example, breadcrumbs – a small link path that helps a user know where they are on your site – are sometimes removed from mobile sites to save on space. Consider whether the advantage of saving that space is worth a loss of clarity for your site structure.


Mobile-first optimisation is coming for everyone and you only have a few weeks left to prepare. While, like any SEO, mobile optimisation should be an on-going process, the more you can do in advance, the fewer negative effects you’re likely to see from such an update.

For a more in-depth look at mobile-first indexing best practices, read Google’s full guide.

If you’d like support with your mobile-optimisation, or any other element of Search Engine Optimisation, please get in touch.

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