The Impact of First Input Delay on User Experience and How to Improve it

The user experience of a web page is critical to its success. It affects everything from the number of visitors to the conversion rates and overall satisfaction of the users with the site. One key performance metric that measures the user experience is First Input Delay.

What is First Input Delay?

First Input Delay (FID) is a critical performance metric that measures the responsiveness of a website, it is the time between when a user first interacts with a page (such as clicking a link) and when the browser is able to respond to that interaction.

A low First input Delay score is important for providing a good user experience, as it ensures that the website will respond quickly to user interactions. This leads to a higher level of user satisfaction and engagement.

According to WebPageTest’s latest statistics from February 2023, about 32% of websites have a first input delay (FID) of 100ms or more which means it needs serious improvements, these 32% of websites due to high FID scores give a bad user experience and overall bad SEO rankings.

We can get this number using the CrUX (chrome user experience) dataset and the BigQuery tool link to the dataset.

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Significance of FID as an SEO (Search Engine Optimization) Keyword

The significance of First Input Delay (FID) as an SEO keyword lies in the fact that it is a crucial aspect of technical SEO and page speed. 

Technical SEO refers to the optimization of a website’s infrastructure and code to make it more easily crawlable and indexable by search engines. One of the key elements of SEO is page speed, which is the amount of time it takes for a page to load in a user’s browser. A slow page speed can lead to a poor user experience and a decrease in the website ranking in search engine results pages (SERPs).

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How Does First Input Delay Work?

When a user interacts with a page, the browser must process the event, run any relevant JavaScript execution and update the DOM before it can respond to the interaction. The process can take time and the delay between the user interaction and the browser response is the First Input Delay.

FID is measured in milliseconds and is calculated as the time between the user interaction and when the browser is able to respond to it. The lower the First Input Delay value, the better the user experience.

A good First Input Delay score ensures that the website will respond quickly to user interactions, leading to a higher level of user satisfaction and engagement.

Factors Contributing to High First Input Delay Scores

Large JavaScript Files:

JavaScript code is essential for many dynamic and interactive elements on a website, such as forms, animations, and navigation. However, large JavaScript files can slow down the browser and increase the FID score. There are various ways to minimize the effect of JavaScript to lower the First Input Delay score which will be discussed in further sections.

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Slow Server Response Times:

Slow server response times can also contribute to a high First Input Delay score, as the browser must wait for the server to respond before it can process the user interaction.

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Complex DOM Updates:

The Document Object Model (DOM) is the structure of a web page and represents how the element on the page interact with each other. Updating the DOM can be slow and complex, especially if the updates are frequent or require more elements to change. This can in turn increase the FID.

Resource-Intensive Images and Videos:

Images and videos can take up a lot of resources and slow down the browser, large images and videos take longer to load adding the time it takes for the browser to respond to user interaction, this can lead to a slow and unresponsive experience to users, leading to a higher FID score. 

Third-Party Scripts:

Third-party scripts such as analytics and advertising, and social media, can also contribute to a high FID score. These scripts can add additional resources that must be loaded, processed, and executed before the browser can respond to user interaction. This can lead to longer response times and poor user experience. 


How is FID Measured?

Measuring First Input Delay is typically done by real-world testing using real users, by logging the time from when a user first interacts with the page to when the browser is able to respond and then testing its interactivity. The measurement tool for measuring the First Input Delay is usually google lighthouse.

What is a Good First Input Delay Score?

A good First Input Delay score is considered to be less than 100 milliseconds. A low FID score indicates that the website is responsive to user input and provides a smooth user experience. 

Optimizing FID 

Optimizing First Input Delay (FID) is crucial for improving user experience and website performance. The following are some of the practices for optimizing FID.

Minimize JavaScript and Other Resources : 

Reduce the amount of JavaScript tasks and other resources required to load a page to improve the time it takes for the browser to respond to user interactions. This can be achieved by combining and minifying JavaScript and CSS files, reducing the number of HTTP requests, and using resource-efficient images and videos, alternatively, tools like RabbitLoader can help minimize the amount of JavaScript required for page load automatically streamlining the process for you.

See more: Defer Loading jQuery in WordPress

Reduce the Size of Large Files : 

Large files can significantly slow down a website and increase the FID time, by reducing the size of the files you can reduce the time it takes for the browser to respond to user interactions and improve FID. This can be done manually by compressing them or using more efficient file formats. Or RabbitLoader can help you optimize the size of these files automatically, ensuring that your pages load quickly and efficiently.

Minimize DOM Complexity : 

The more complex the Document Object Model (DOM) of a website, the longer it takes for the browser to process user interactions. To minimize DOM complexity, use techniques such as avoiding excessive nesting, reducing the number of elements on a page, and using CSS instead of JavaScript to manipulate DOM. this can be done manually or by tools like RabbitLoader which can update DOM automatically allowing for a faster and a more responsive experience for your user.

Implement Lazy Loading : 

Lazy loading is a technique that only loads resources such as images and videos when they are needed. This can significantly reduce the amount of data required to load a page and improve the time it takes for the browser to user interaction and reduce the First Input Delay time.

Minimizing Third-Party Scripts : 

Third-party scripts such as advertisements, analytics, and social media widgets can slow down a website and increase its First Input Delay time, To minimize the impact of third-party scripts manual optimization can be done by reducing the scripts used, implementing lazy loading, and using resource-efficient scripts. This can either be done manually or tools like RabbitLoader can automatically do this for you improving your website’s First Input Delay score.

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Using Fast Hosting Solutions : 

A slow hosting solution can significantly impact the time it takes for a website to load and increase the time it takes for a website to load and increase the time it takes to respond to user interactions. To optimize FID, use a fast hosting solution with low latency and high bandwidth. 

Use a Content Delivery Network (CDN) : 

A Content Delivery Network (CDN) can improve the time it takes for a website to load by caching and serving content from multiple locations around the world. By using a CDN you can reduce the time it takes for the browser to respond to user interactions and improve the First input delay.

These optimization techniques can help you improve the performance of your website and reduce the First Input Delay (FID) to provide a better user experience. However, it is important to note that the First Input Delay is just one of several Core Web Vitals and to provide a high-quality user experience, its necessary to optimize all the web vitals including the Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and Total Blocking Time (TBT).

Apart from these optimization methods, there are some other methods as well listed below, the below-listed methods revolve around implementing the above-mentioned methods. 

Defer Unused Scripts:

Any unused scripts should be deferred until they are needed. This can be achieved either by splitting large scripts into smaller ones or by using code splitting and loading scripts on demand. 

Minimize Main Thread Work: 

To minimize the main thread work, you can use lazy loading to defer the loading of images and other heavy resources until they are needed. 

Minimize DNS Lookups: 

A DNS lookup is the process of finding the IP address associated with a domain name. By reducing the number of DNS lookups, you can speed up your website’s load time. You can achieve this by reducing the number of third-party scripts and plugins used on your website.


Use Browser Caching: 

Browser caching allows your website to save frequently accessed resources to a cache, reducing the time required to load the resources. You can leverage browser caching by using expires headers, cache control headers, and ETags.  


What is Meant by Deferring?

Defer means the process of delaying the loading of a certain resource, such as a JavaScript file until it is needed. By deferring the loading of non-critical resources, it reduces the amount of JavaScript that needs to be parsed and executed during page load, resulting in faster page load times and a good First Input Delay score.

What is a DNS Lookup?

DNS lookup is the process of resolving a domain name to its corresponding IP address. When a user enters a website’s domain name into their browser, the browser sends a request to a DNS server to resolve the domain name to its IP address. The IP address is then used to access the website’s server, where the website is hosted. This is an essential part of the process of accessing a website as it allows the browser to find and connect to the correct server hosting the website.

What is the Core Web Vital?

Core Web Vitals are a set of metrics defined by Google that measure the quality of user experience on websites. They include 3 main aspects: loading speed, interactivity and visual stability the Core Web Vitals metrics are: 

Largest Contentful Paint (LCP)

First Input Delay (FID)

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Cumulative Layout Shift (CLS)

What is the Largest Contentful Paint (LCP)?

Largest Contentful Paint (LCP) is a web performance metric that measures the loading performance of a page. It specifically measures the time taken for the largest element visible within the viewport ( such as an image or text block ) to fully load and become visible to the user. LCP is one of the three core web vital metrics.

What is Cumulative Layout Shift (CLS)?

Cumulative Layout Shift (CLS) is a metric that measures the visual stability of a website. It is one of the three Core Web Vitals.

 CLS measures the amount of unexpected movement of page content, such as images or text, while the page is loading, this movement can cause the users to accidentally click on the wrong element, which can have a negative impact on the overall user experience, the goal should be to have CLS score of 0, indicating no unexpected movement which leads to smoother user experience. 

What is Total Blocking Time (TBT)?

Total Blocking Time (TBT) is a performance metric that measures the total amount of time a page is blocked from responding to user input, such as scrolling or clicking links, TBT is expressed in milliseconds and is calculated as the sum of all periods of time and where the browsers main thread of the page was blocked for more than 50 milliseconds. 

This metric is an important factor in determining the overall user experience of a website, as it measures the interactivity of the page and how quickly it can respond to them. Higher the TBT score the more negative the impact on the user experience and leading to a lower conversion rate and decreased traffic to a website. 

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Google’s Core Web Vital is monitored by using various tools and techniques, including google analytics and google page speed insights. 

Google Analytics can track and report on the user experience metrics of a website, including core web vital, this allows website owners and developers to monitor the performance of their site and identify areas for improvement.

PageSpeed insight is a tool that analyzes the performance of a website and provides recommendations for optimization. It also reports on the core web vital for a given page.

In addition to page speed insight and google analytics, developers can use a variety of performance monitoring, real user monitoring, and testing tools to measure the core web vital and identify areas for optimization. By monitoring these key performance metrics, website owners and developers can ensure that their sites provide the best possible user experience.


In conclusion, optimizing First Input Delay (FID) is crucial for providing a great user experience and improving the overall performance of a websites FID, along with other googles Core Web Vitals, are important indicators of a websites page experience and are increasingly being used by google to rank websites in google search results by google page experience.

 Utilizing tools like google page speed insights, google lighthouse, and google analytics, websites can reduce their First Input Delay scores and improve the performance and user experience for real users.

By providing a responsive and fast website, businesses can not only improve user satisfaction and engagement but also boost their visibility on google searches and achieve better conversion rates. Overall paying attention to FID is an important aspect of website optimization and should not be overlooked.