The third and final metric of Google’s Core Web Vitals is First Input Delay (FID). It measures web page interactivity – how quickly your website responds to the user input. FID refers to UX-related signals that reflect how quickly your website shows the expected result when you perform some action on the website. 

Compared to other web performance metrics, FID is unique in a way that it exclusively measures how real users perceive your web page in the field. It means it cannot be reproduced and tested in the lab environment.  

First Input Delay (FID)

FID Explained – Interactivity Speed & Responsiveness of a Website 

FID is calculated as the time your browser takes to respond to any of the following common interactions.  

  • Tapping on the screen
  • Pressing a CTA button 
  • Clicking on a link 
  • Typing into contact-form field
    Get a Response

FID is a field metric that gauges how quickly your browser loads the elements you have interacted with and the response time of the web page to react to these interactions. This input delay occurs when your browser’s main thread is occupied by other long tasks (e.g. anything above 50 milliseconds) and hence, unable to respond to the user request. You will notice a delay and the web page will be perceived as sluggish and unresponsive.  

First input delay

Measured in milliseconds, FID does not include scrolling and zooming on the page. 

Which pages are considered fully interactive by Google? 

A fully interactive page should fulfill the following requirements: 

  • The page must display useful content (measured by First Contentful Paint
  • The visible page elements with registered event handlers
  • The page should respond within 50ms to user interactions

FID Score Range: 

FID indicates the delay which the user experiences when interacting with different web page elements. Ideally, for a good user experience, you should aim to maintain your site’s FID score equal to 100ms or less. It means users will not even notice a delay. 

Good

Average

Poor

≤ 100 ms

100-300 ms 

≥ 300 ms

Good FID Score: 

Good FID Score

Total blocking time

Result of ArhamSoft.com  

Poor FID Score: 

Poor FID Score

Total blocking time

Result of Theguardian.com

Note: You can view more details about Total Blocking Time in the Chrome Dev Tools Performance panel.  

What is Total Blocking Time? 

The Lab tools like WebPage Test only provide the Total Time Blocking – measuring the website loading response. FID is measured in terms of Total Time Blocking, which should be as low as possible to ensure that a web page is usable. This important lab metric measures the website load responsiveness and gives a rough idea about how your website may perform in terms of FID.   

FID vs TTI: 

TTI stands for Time to Interactive metric, which is used to calculate the time a web page takes to become fully interactive. FID and TTI are often correlated because both metrics refer to the measuring aspects of web page interactivity.  

However, both differ in a way that TTI only tells us the duration for the web page to become interactive while FID also tells the duration of the web page to respond to the user interaction. Your web page can achieve a good FID score despite having a bad TTI score. 

FID and SEO: 

Everyone loves using fast and responsive websites. And, FID is a key indicator that refers to the user’s first impression of the interactivity speed of a web page and its responsiveness. When FID is high, it allows you to know that your website users are waiting too long and this is not good for your site’s SEO performance. 

A good FID score means a user is more likely to stay on your site, consume more content, and happens to be a potential lead. With a reader spending more time on your website, your site’s bounce rate will be improved with the maximized chances for more sales and revenue generation.  

FID helps optimize your website for better search engine rankings. Poor FID score means poor bounce rate causing decreased page sessions. The input delays can make you lose lots of potential customers because users tend to immediately leave a website that does not respond fast. Certainly, you cannot afford losing your marketing efforts and ROI. So, it’s essential for your website to have improved FID. 

What Contributes To Poor FID? 

Anything that results in unnecessary time between user input and your page’s response to that action contributes to a low FID. Here are some of the primary causes of poor FID.

  • Long tasks (browser must pause to run an event)
  • Long JavaScript execution  
  • Sub optimal, heavy codes 
  • Render-blocking JavaScript

One of the key reasons is JavaScript execution of heavy files. When a website loads, but doesn’t respond to your performed action, then it is more likely to load some JS elements or files. It means the main thread gets busy with loading some other heavy JS files and the browser will respond after completing this JS execution.

Moreover, heavy codes on your site and that are also not optimized can contribute to poor FID score. 

All JS files are render-blocking which means the browser will stop all the current tasks and start loading the JS files it encountered. Until the loading of JS files is completed, the browser will not respond to the user input – the user must wait for the web page response. So, better remove all unused JS files and elements from your website for an improved FID score. 

Measuring FID: 

Since FID is different from other two metrics of Core Web Vitals (LCP and CLS) and measures the real user interaction and experience, this metric requires actual users to engage with the web page. 

FID can be measured in more detail using the following field monitoring tools.

You can examine each web property by heading to Google Search Console and assessing your current Core Web Vitals. 

Optimizing FID: 

For all the four FID issues, there are 4 simple solutions. 

  1. Optimize third-party code, tags and analytics to reduce their impact on web page interactivity. 
  2. Minimize the main thread work by reducing design layout and styling complexities and freeing it up from non-critical operations. 
  3. Decrease JS execution time by removing heavy styling and unused files. Also, only render the minimal code required.
  4. Keep transfer sizes small and request counts low so that users will get the most important and critical information on the web page’s first load.

This Google guide will give you more information about the actionable steps to improve your FID score. 

Summing Up:

First Input Delay (FID) is a really important web performance metrics that reflects the real-world page experience of the actual users. Google values fast and responsive websites and page’s loading speed is already a significantly important attribute in its ranking algorithm. Slow websites result in user frustration leading to decreased page sessions and high bounce rate that will bring such websites down in the search engine page rankings. Your SEO will be negatively affected by the poor FID score of your website. Optimize your website to keep FID score lower than 100ms – necessary to move your site up in the Google rankings. 

ArhamSoft (Pvt) Ltd. is an ISO-certified software development company that helps businesses protect and improve their website’s search ranking signals by fixing all development-related FID issues.

Read more about the other two Core Web Vitals:

Cumulative Layout Shift (CLS)

Largest Contentful Paint (LCP)