Core Web Vitals: First Input Delay – What It Is and How to Improve It for SEO

“Core web vitals” is a set of core webpage functionalities that impact user experience. In May 2020, Google announced that core web vitals would be incorporated into a ranking algorithm update called page experience, set to hit in 2021.

At the time of writing, the current set of core web vitals includes:

  • Largest contentful paint
  • First input delay
  • Cumulative layout shift

In this article, No. 8 in our series covering the Page Experience update, I’ll discuss first input delay, or FID:

What Is First Input Delay (FID)?

FID measures load responsiveness, which is how quickly a webpage loads and executes so that the user can interact with the page.

Google discusses FID here:

First Input Delay (FID) is an important, user-centric metric for measuring load responsiveness because it quantifies the experience users feel when trying to interact with unresponsive pages—a low FID helps ensure that the page is usable. …

FID measures the time from when a user first interacts with a page (i.e. when they click a link, tap on a button, or use a custom, JavaScript-powered control) to the time when the browser is actually able to begin processing event handlers in response to that interaction.

Google cites two important reasons why the first input delay is important:

  • The first input delay will be the user’s first impression of your site’s responsiveness, and first impressions are critical in shaping our overall impression of a site’s quality and reliability.
  • The biggest interactivity issues we see on the web today occur during page load. Therefore, we believe initially focusing on improving site’s first user interaction will have the greatest impact on improving the overall interactivity of the web.

Keep in mind that FID will not apply to every situation, as Google points out here:

Not all users will interact with your site every time they visit. And not all interactions are relevant to FID … How you track, report on, and analyze FID will probably be quite a bit different from other metrics you may be used to.

How Is First Input Delay (FID) Measured?

FID measures the first impression of your site’s interactivity and responsiveness. It analyzes things like clicks, taps and key presses, which fall under the “responsiveness” category. It does not measure things like scrolling and zooming, which are related to animation.

Google recommends webpages aim for an FID of less than 100 milliseconds, which means the page would be able to respond to an interactive event within that time frame. In order to be considered “good,” Google’s threshold should be met 75 percent of the time, segmented across mobile and desktop devices. You can learn more about how Google creates thresholds here.

FID score range from Google.
Google’s FID score

While the official threshold is 75% of pages loaded, Google says that for FID in particular, they “strongly recommend looking at the 95th to 99th percentiles, as those will correspond to the particularly bad first experiences users are having with your site. And it will show you the areas that need the most improvement.” This is true for both desktop and mobile users.

Keep in mind that the 75% is the sample. So, for example, if your site has 1,000 pages and Google indexes all of them, then 750 of them would need to have a good FID for the whole site to be classified as having a good FID. Google is saying that in reality, it should be 98% or 99%.

For developers, it’s important to understand that Google only measures the delay in event processing, not the “event processing time itself nor the time it takes the browser to update the UI after running event handlers.”

In other words, Google only measures how long the browser takes to start executing the event process. So, if you click on a link, it’s the delay between the time you click and the time the browser starts processing that click.

And when you’re ready to start improving FID, you’ll use tools that can help measure real data in the wild.

How Does First Input Delay (FID) Impact SEO?

FID is another way to speed up your webpages for visitors. Consider that fast page load times is already a best practice for SEO and a current ranking factor. FID helps keep visitors on your site because they can interact with the content faster.

When people bounce from your site, they may never come back and you can lose potential revenue. Not only that, but a sluggish site can also impact your rankings. That’s because Google’s AI, RankBrain, may take into account how a user engages with the search results.

Over time, if a website has enough visitors who go to the page from the search results and bounce back quickly, this could indicate they didn’t find what they were looking for. Because RankBrain’s goal is to analyze and serve the most relevant search results, rankings could suffer.

The good news is that most sites may already be OK when it comes to FID. In a study by Screaming Frog, 89% of mobile and 99% of desktop URLs fell within the threshold. The average was around 56 milliseconds on mobile and 13 milliseconds on desktop.

When looking at FID and search rankings correlation, Screaming Frog says that there’s much less of a correlation than for other core web vitals. But you need to recall that 2021 is when this becomes an important factor, and we would not expect an impact yet.

First input delay (FID) data from ScreamingFrog study.
“How Many Sites Pass the Core Web Vitals Assessment?,” Screamingfrog.co.uk

How Do I Improve My First Input Delay (FID) Score?

Google provides tools to measure FID in the field, including:

You can also measure FID with the web-vitals JavaScript library, and you can learn more about that here. But most website publishers aren’t going to do this. It’s only useful if you have your own reporting or if you want to build it into other reports.

The primary cause of a bad FID score is heavy JavaScript execution. So be sure to optimize how “JavaScript parses, compiles, and executes on your web page will directly reduce FID,” says Google.

Reducing the amount of JavaScript and/or optimizing the running of JavaScript has always been a good idea for SEO. It reduces page bloat, improves page performance and also provides Google an easier path to index the correct content. That’s because Google will not have to process as much JavaScript to figure out what it needs.

In our experience, the more you can give Google what it needs right away, without having to process too many things, the better Google will index your site the way you think it should be indexed. Indexing is hugely important for SEO as it influences what pages Google determines are valid or not.

To optimize the FID score, Google recommends running a Lighthouse performance audit and looking at the opportunities uncovered, but gives more detail on how to optimize JavaScript here.

Find out more about the coming update by reading our Page Experience series:

  1. What’s the Page Experience Update?
  2. How to Make a Mobile-Friendly Site
  3. Intrusive Interstitials & Why They’re Bad for SEO
  4. Safe Browsing to Protect Your Website, Visitors & Ranking
  5. HTTPS for Users and Ranking
  6. Core Web Vitals Overview
  7. Core Web Vitals: LCP (Largest Contentful Paint)
  8. Core Web Vitals: FID (First Input Delay)
  9. Core Web Vitals: CLS (Cumulative Layout Shift)

If you need technical SEO assistance, please contact us for a free consultation and let’s talk.

Bruce Clay is founder and president of Bruce Clay, Inc., a global digital marketing firm providing search engine optimization, pay-per-click, social media marketing, SEO-friendly web architecture, and SEO tools and education. Connect with him on LinkedIn and other social networks from Bruce's author page.
Comments (7)
Filed under: SEO — Tags: ,

7 Replies to “Core Web Vitals: First Input Delay – What It Is and How to Improve It for SEO”

Code Optimization is an important part of on-page SEO.

interesting article, I think I need to increase the performance of my website

What is the difference between fid and complete page load time.

These are good articles – helpful – thank you :-) *we are beginning to focus more intently on these core web vital stats now :-)

Google PageInsight Score is tested from American servers, how are Australian websites suppose to receive accurate readings when they don’t allow for location selection?

Paula Allen

Daniel: I asked our in-house expert on technical matters, and here’s his answer regarding an Australian website.

You’re right; PageSpeed Insights probably won’t give you the most accurate data. But, the Core Web Vitals are based on more than one run of that report; they are based on thousands of impressions of “field data” that is aggregated into the Chrome User Experience Report, or CrUX. That data is available from Google via BigQuery; there’s a handy write-up on how to create a Data Studio Dashboard from that data if you want a report on it: https://web.dev/chrome-ux-report-data-studio-dashboard/.

Because that data is only updated monthly, it won’t show you improvements to your site as you are making them or testing them. In that case, I would either run the Lighthouse report inside of the Chrome Dev Tools, or I would run the the web vitals package directly on your site and log the stats to the JavaScript Console or another place. You don’t even need to download and install it; you can run it from a CDN and print the values to the console: https://github.com/GoogleChrome/web-vitals/#load-web-vitals-from-a-cdn. Lighthouse may also be using some data from a US server, but I believe most of it comes from your browser.

Interesting. I just ran a Page Speed test on https://blog.google and they get a 45 score in mobile and 77 on desktop. #irony

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