First Input Delay: Meaning And How To Make An Optimization

Experienced E-commerce Agency for Magento/ Adobe Commerce/ Shopify/ Shopware Development

For online businesses and website owners, delivering a seamless and responsive user experience has become essential.

Users are accustomed to immediate gratification and anticipate fascinating, highly interactive websites. However, in practice, a lot of websites fall short of providing this seamless experience and are frequently hampered by annoying delays that prevent user interactions.

One of the crucial metrics that directly impact user experience is First Input Delay (FID). FID measures the time it takes for a site to respond to the very first user interaction, such as clicking a button, tapping on a link, or filling out a form.

This post will offer helpful insights and doable actions to help you significantly improve user experience and maintain your website ahead in today’s competitive digital landscape, whether you’re an experienced developer or fresh to the field of web design.

Table of Contents

What is First Input Delay?

First Input Delay (FID) is a web performance metric that measures the responsiveness of a website or web application to user interactions. It specifically focuses on the delay between a user’s first interaction, such as clicking a button, tapping a link, or entering data in a form field, and the website’s actual response to that interaction. FID is typically measured in milliseconds.

FID is an essential metric because it reflects the time it takes for the browser to process the user’s input and begin executing the associated JavaScript code. A high FID indicates a noticeable delay between the user’s action and the website’s response, resulting in a less fluid and interactive user experience. On the other hand, a low FID signifies that the website is responsive and can quickly process and react to user input.

First Input Delay meaning

FID differs from other web performance measures like First Contentful Paint (FCP) and Largest Contentful Paint (LCP), which emphasize the visual aspects of page loading. FID focuses on the impact of website responsiveness on user engagement and satisfaction and specifically addresses the delay in user interaction.

Website owners, creators, and designers consider FID a crucial metric for evaluating and enhancing user experience. Website operators may ensure a seamless, engaging, and highly responsive website that keeps users happy and engaged by comprehending the variables that contribute to user interaction delays and putting effective measures to reduce FID into practice.

The process of the First Input Delay

The First Input Delay (FID) process encompasses several stages between a user’s interaction and the website’s response. This is the typical process of FID:

  • User interaction: The process begins when a user acts on a web page, such as clicking a button, tapping a link, or inputting data. This action triggers an event that the website needs to handle.

  • Event handling: The browser captures the user’s event and passes it to the website’s event-handling code, usually written in JavaScript. This code is responsible for processing the user’s action.

First Input Delay process

  • Main thread blocking: If the website’s main thread is occupied with other tasks like rendering or executing JavaScript, it may be unable to promptly process the user’s event. This delays the user’s interaction and the website’s response, resulting in a higher FID.

  • JavaScript execution: When the main thread becomes available, the event-handling code starts executing. This code performs various operations, such as updating content, making server requests, or triggering animations. The duration of JavaScript execution directly influences the FID.

  • Time to interact: The FID measurement concludes when the website becomes interactive. Time to Interactive (TTI) is another performance metric that measures the time it takes for a web page to become fully interactive and promptly respond to user interactions. Reducing delays in event handling and JavaScript execution contributes to achieving a lower FID and faster TTI.

It is crucial to recognize and take action against the causes of event handling and JavaScript execution delays to reduce First Input Delay. Developers can improve the performance of their code, reduce main thread blocking, and prioritize important operations.

Code separation, lazy loading, and asynchronous JavaScript execution are further techniques that can boost FID by ensuring quicker page interaction and event processing. A more responsive and interesting user experience is the outcome of these optimizations.

Why is First Input Delay important?

First Input Delay (FID) is significant because it affects how users interact with websites and web applications. Here are some major arguments in favor of the importance of FID:

  • User perception: FID plays a crucial role in how users perceive the responsiveness and interactivity of a website. A noticeable delay between a user’s action and the website’s response creates a sense of unresponsiveness, frustration, and poor user experience.

  • User engagement: A website with a low FID tends to encourage user engagement and interaction. When users can effortlessly navigate, click buttons, fill out forms, or perform other actions without experiencing delays, they are more likely to stay engaged and explore further.

Why is First Input Delay important?

  • Conversion rates: FID directly influences conversion rates, particularly for websites that rely on user interactions to complete transactions or achieve specific goals. Users are more likely to abandon a website or abandon a purchase if they encounter delays and unresponsiveness during critical actions like adding items to a cart, initiating a payment, or submitting a form. Optimizing FID helps to minimize friction and maximize conversion rates.

  • Search Engine Optimization (SEO): FID is also vital in search engine rankings. Search engines like Google consider website performance metrics, including FID, as part of their ranking algorithms. Websites with better FID are more likely to rank much higher in search results, resulting in increased visibility, organic traffic, and potential business opportunities.

  • Mobile experience: With the growing prevalence of mobile devices, FID becomes even more critical. Mobile users often encounter network limitations, slower processing power, and varying device capabilities. Optimizing FID ensures a smooth and responsive mobile experience, catering to the needs and expectations of mobile users.

What is a good First Input Delay (FID) score?

First Input Delay (FID) scores of less than or equal to 100 milliseconds (ms) are often regarded as favorable. A website or web application that receives ratings below this cutoff responds to user interactions rapidly, resulting in a responsive and seamless user experience.

It’s crucial to remember that FID ratings might change depending on the complexity of the website, the user’s device and network settings, and the precise user interactions being analyzed. But generally speaking, striving for an FID score of 100 ms or below is thought to be a good goal.

First Input Delay good score

Google’s Core Web Vitals, a set of performance metrics that Google uses to assess website user experience, categorizes FID scores as follows:

  • Good: FID ≤ 100 ms

  • Needs Improvement: FID between 100 ms and 300 ms

  • Poor: FID > 300 ms

While achieving an FID score below 100 ms is ideal, any improvement in FID can contribute to a better user experience. Therefore, even if your FID score falls within the “Needs Improvement” range, working towards reducing it can still yield noticeable benefits.

It’s worth mentioning that FID scores should be analyzed in conjunction with other performance metrics, such as Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS), to gain a comprehensive understanding of the overall user experience.

What is the reason for a low FID score?

A website or web application with a low First Input Delay (FID) score is extremely responsive and can react quickly to user interactions. A low FID score may be attained for a number of reasons, including:

  • Efficient event handling: The website’s event-handling code is optimized and performs efficiently. It quickly captures and processes user interactions, minimizing the delay between the user’s action and the website’s response.

  • Minimal main thread blocking: The website’s main thread, which handles various tasks like rendering and executing JavaScript, experiences minimal blocking. This allows the event-handling code to execute without significant delays, resulting in a low FID score.

  • Optimized JavaScript execution: The website’s JavaScript code is optimized for performance. It executes efficiently, without excessive computations or time-consuming operations, leading to faster event processing and a lower FID score.

What is the reason for a low FID score?

  • Prioritized critical tasks: Critical tasks that directly impact user interactions are given priority in the website’s code execution. The website can achieve a low FID score and provide a highly responsive user experience by ensuring that essential operations are handled promptly.

  • Effective resource loading: Resources, such as scripts, stylesheets, and images, are loaded in an optimized manner. Lazy loading techniques, code splitting, and efficient caching strategies can help reduce the amount of data that needs to be loaded initially, minimizing potential delays in event handling and improving FID.

  • Network and server optimization: Fast network connections and optimized server response times contribute to a low FID score. When the browser can quickly communicate with the server and fetch necessary resources, the overall responsiveness of the website improves, resulting in a lower FID.

  • Device performance: The user’s device and browser capabilities also play a role in achieving a low FID score. More powerful devices with faster processors and optimized browser implementations can process user interactions more swiftly, contributing to a better FID.

4 tools for evaluating your First Input Delay

1. Web Vitals JavaScript Library

Web Vitals JavaScript Library

The Web Vitals JavaScript Library is a lightweight JavaScript library developed by Google. It simplifies collecting and reporting web performance metrics directly within web applications, including First Input Delay (FID).

This tool allows developers to track and monitor FID scores over time, enabling them to identify performance issues and optimize their applications accordingly.

2. Chrome User Experience Report

Chrome User Experience Report

The Chrome User Experience Report is a public dataset available through Google BigQuery. It consists of anonymized, real-world performance data collected from millions of websites that use the Chrome browser. The CrUX dataset provides aggregated metrics, including FID, based on actual user experiences.

By analyzing CrUX data, website owners and developers can better understand how their FID scores compare to the overall web ecosystem and make data-driven decisions for optimization.

3. Search Console Core Web Vitals Report

Google Search Console

Google Search Console is a web service that provides website owners with data and insights regarding their website’s presence in Google Search results. Within Search Console, the Core Web Vitals Report specifically focuses on the three core web vitals, including FID.

It provides a detailed analysis of FID scores for specific URLs on the website, highlighting areas that require attention and optimization.

4. Page Speed Insights

PageSpeed Insights

As a tool developed by Google, PageSpeed Insights assesses the performance of web pages on both desktop and mobile devices. It analyzes various performance metrics, including FID, and provides a detailed performance report for the tested webpage.

PageSpeed Insights uses data from the Chrome User Experience Report and Lighthouse, another performance auditing tool, to generate insights and recommendations. The tool scores the web page’s performance, provides suggestions for optimization, and offers a field data view based on real-world usage metrics.

7 ways to optimize First Input Delay

Optimizing First Input Delay (FID) is crucial for improving website performance and delivering a responsive user experience. Here are seven ways to optimize FID:

Break up large tasks into smaller ones

Dividing large tasks into smaller chunks allows the browser to process them more efficiently. By optimizing JavaScript code and splitting long-running tasks, you can reduce the impact on the main thread, leading to faster event handling and a lower FID.

Activate progressive loading

Implementing progressive loading techniques like lazy loading images and deferring non-critical scripts can significantly improve FID. By loading essential elements first and deferring the loading of non-critical elements until after the initial page load, you reduce the workload on the main thread and provide a faster interactive experience for users.

Switch logic to the server side

Moving computationally intensive tasks or business logic to the server side can help reduce the amount of JavaScript execution required on the client side. By offloading tasks to the server, you can minimize the processing time needed on the client, resulting in a faster response to user interactions and improved FID.

Ways to optimizing First Input Delay

Produce content automatically

Avoid relying on user interactions to trigger the production of content. Instead, anticipate and automatically generate content in advance. This approach ensures that the necessary content is readily available when users interact with the page, minimizing delays and improving FID.

Review the execution of third-party scripts

Third-party scripts, such as analytics or tracking codes, can impact FID if they’re not optimized. Evaluate the necessity of each third-party script and consider asynchronous loading or delaying their execution until after the initial page load. Additionally, regularly review and update third-party scripts to ensure they’re optimized for performance.

Make use of web workers

You may free up the main thread for user interactions by using web workers to shift computationally demanding activities to background threads. You can increase FID by using web workers to complete time-consuming tasks without stopping the main thread.

Ways to optimizing First Input Delay

Review the use of polyfills

Polyfills enable the use of modern web features in older browsers. However, some polyfills can be resource-intensive and impact FID. Evaluate the necessity of each polyfill and consider selectively loading them based on browser support. By reducing the use of unnecessary polyfills, you can improve FID for users with older browsers.

By putting these optimization techniques into practice, you may lessen the First Input Delay and improve user experience as a whole. FID should be measured and observed frequently to track advancements and spot any areas that need more optimization.


In conclusion, optimizing First Input Delay (FID) is essential for creating a highly responsive and user-friendly website. You can enhance user satisfaction, engagement, and conversion rates by reducing the delay between user interactions and the website’s response.

In this article, we explored the meaning of FID and the process behind it. We learned that FID encompasses various stages, including user interaction, event handling, main thread blocking, JavaScript execution, and time to interact. Understanding this process helps us identify potential areas for optimization.

By prioritizing FID optimization, website owners and developers can deliver an exceptional user experience, improve search engine rankings, and achieve higher conversion rates. Remember to regularly assess FID scores, measure the impact of optimizations, and stay up to date with best practices to ensure ongoing performance improvements.

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Vinh Jacker
Hello, I'm the Chief Technology Officer of Mageplaza, and I am thrilled to share my story with you. My deep love and passion for technology have fueled my journey as a professional coder and an ultra-marathon runner. Over the past decade, I have accumulated extensive experience and honed my expertise in PHP development.
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