First Input Delay (FID) is a Core Web Vitals metric defined by Google that measures the interactivity and responsiveness of web pages. When calculating a PageSpeed score for a URL, the First Input Delay (FID) value represents the time lag between the first user interaction with the page elements and when the web browser is actually able to process the user request.
Core Web Vitals prioritizes interactivity in the user experience (UX), which is negatively impacted by long page load times that decrease the responsiveness of page elements. Unlike other Google PageSpeed metrics, the First Input Delay (FID) value is totally reliant on field data from users. The calculation of FID requires a real user to interact with the web page directly.
What is First Input Delay (FID)?
First Input Delay (FID) is one of the three metrics that are used in the Core Web Vitals test. The other two factors are Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS). The First Input Delay (FID) value is determined by Chrome User Experience Reports representing the field data from web browsers that have accessed the page historically. Google refers to this as Real User Monitoring (RUM). The calculation of the Google PageSpeed score by Lighthouse does not explicitly include the FID field data, but provides the TTI estimate from lab data.
The first input is defined as events from user interactions like mouse clicks, screen taps, and keyboard activity. The delay is calculated by measuring the time between the point when the first input event is recorded by the user and the main thread is fully idle or the browser is able to process the request. Note that this is the time that it takes for the browser to start processing the request, rather than the interactive response itself. In the example of the use of a dropdown menu, this is not recorded as the time required for the browser to open the dropdown, but rather the time that it takes for the browser to be able to “understand” the visitor clicked on it.
User experience (UX)
The PageSpeed score for a web page is calculated on the basis of statistical metrics that measure the perceived load speed, load responsiveness, runtime responsiveness, visual stability, and smoothness of the user experience (UX). The RAIL model divides the life cycle of a web application into the categories of response, animation, idle, and load for performance analysis. These factors allow the user experience to be standardized for assessment in SEO.
Not all of the Core Web Vitals information is included in the calculation of a PageSpeed score. The two tests are designed to complement each other. Core Web Vitals are primarily intended to evaluate whether a URL delivers its content and becomes interactive in a time under 5 seconds in production. The key performance metrics of the assessment are related to the user experience (UX). Google recommends that a web page delivers a visible response within 100 ms, animates a frame within 10 ms, and processes user input events within 50 ms.
In practice, the Core Web Vitals and PageSpeed reports should both be used for SEO when evaluating the user experience (UX), as improvements made to one will be carried over to the other beneficially. However, professionals should recognize that they are not identical standards. Google prioritizes the user experience (UX) for search engine rankings, combining CWV analysis with factors related to content, keywords, URL structure, titles, etc. in their algorithm weighting system. Web pages need to optimize all of these factors to rank favorably in SERPs.
What does FID measure?
First Input Delay vs. Time to Interactive
The First Input Delay (FID) metric represents the average time for desktop and mobile views to become fully responsive on a web page, including user access by different endpoint devices and connection speeds. Long first input delays typically occur between the First Contentful Paint (FCP) rendering and the Time to Interactive (TTI), primarily because the web page has downloaded some of its display and GUI content but isn’t yet reliably interactive for users.
To illustrate how this can happen, FCP and TTI have been added to the timeline for SEO analysis. The Time to Interactive (TTI) value is calculated from lab data by Lighthouse and other tools, measuring the length of time required for the page to visually render, fully load all required scripts, and become capable of responding to user input through idleness of the main thread. In contrast to the FID formula, TTI does not require any real user activity on a page to calculate.
What is a good FID score?
Google defines a “good” First Input Delay (FID) score as less than 100 ms of input latency. A FID score of 100 to 300 ms is rated as “needs improvement” and any value over 300 ms is considered to be “poor”. The average of 75% of the users determines the overall rating. With an input latency of less than 85 ms, any click by a user on the interface elements will be experienced as a real-time event. Any FID lags over 100 ms are perceived as being delayed.
Statistical data & threshold value
The Chrome User Experience Report (CrUX) is used in the calculation of Core Web Vitals on the basis of real user experiences across millions of websites. This public dataset includes information on the type of device and speed of connection that the web browsers use to access a URL. Google has determined that the experience of 99% of desktop users and 78% of mobile browsers at the 75th percentile is rated as “good” at the threshold value of 100 ms for FID.
How to measure First Input Delay (FID)?
The First Input Delay (FID) value is calculated from field data that is generated by users who opt in to user experience reporting while navigating the web with the Chrome browser. Response to control activation is measured by recording the initial mouse, keyboard, or touch-pad activity entered by the users on the page and the time delay required for the input to be processed. These values are averaged to the 75th percentile by discarding the outlier values in the data set and the running average of the last 28 days of user activity produces the FID score for the page.
What affects First Input Delay (FID)?
How to improve First Input Delay (FID)?
In most instances, all of the approaches for PageSpeed optimization cannot be implemented on every URL. Some of the SEO techniques require a major change of page structure and content. To reliably improve the FID score, make sure to address the factors below on each webpage:
- The Parsing of HTML and CSS
- The Extraction of Critical CSS
- The Minification of CSS Files
- The Deferment of Non-Critical CSS
The framework that a website is built with can have a significant effect on the page load speed. Sites built with open source CMS platforms like WordPress, Drupal, and Joomla need to adopt automated techniques for PageSpeed optimization through plugin, module, and back-end solutions that implement the recommendations listed above to be successful in improving the FID score. It is especially important to configure web page caching and use a CDN service.
How to fix FID scores for WordPress sites?
Browser caching of UI elements and compression of HTML/CSS files are other important tactics that minimize the total file size of downloads for a WP page. Establishing a cache validator requires WordPress administrators to add cache-control headers with last-modified and etag values so that the browser can determine if content has been modified since the last page load. Cache-control headers allow websites to declare the amount of time that content should remain in the cache before expiring. You may need to edit the .htaccess file for the cache settings to propagate across a WordPress site. Make sure to minify and defer the loading of non-critical CSS files, or inject the code inline for better load times. Automating these tactics across a WordPress site with back-end support will improve the FID score across all of the pages.
10Web Booster is a comprehensive plugin solution for optimizing WordPress websites for Google PageSpeed and Core Web Vitals. 10Web Booster service implements comprehensive front-end and back-end optimization solutions for WordPress that apply the recommendations of the PageSpeed Insights report. 10Web Booster will improve the FID score of production websites automatically without the need for complex configuration of settings in wp-admin.
10Web Booster delivers:
- Image compression and conversion to WebP format
- Lazy-loading of images, iframe content, and videos
- Optimized CSS and web font delivery for displays
- Web server performance optimization for CWV
- Guaranteed 90+ Google PageSpeed Insight scores
10Web Booster increases mobile traffic engagement for WordPress sites, improves page load speeds for better user retention, and leads to higher ecommerce conversion rates in production. Web publishers can sign up to get started with 10Web Booster for free with the choice of complete front-end optimization for Google PageSpeed running on your current hosting solution or high-performance back-end support running on Google Cloud Platform with Booster Pro.