First Input Delay (FID): Definition, Measurement and How to Fix It

We all know how important it is to create a first impression. But when it comes to businesses, digital marketing forms the amplifiers of that first impression, especially taking account of the modern era. The key aspect that stands in this landscape is First Input Delay (FID), a metric to determine how fast your webpage loads when someone clicks on it. In this blog, we will cover all the details related to First Input Delay (FID) and help you understand the complexities of this key performance metrics.  

Table of Contents 

1) What is First Input Delay (FID)? 

2) First Input Delay (FID) in Detail 

3) How to Measure First Input Delay on Your Page? 

4) Differences between the FID and the API 

5) Conclusion 

What is First Input Delay (FID)? 

First-input delay is defined as the time it takes for a webpage to respond when a user first interacts with it, such as by clicking a button or a link. For example, if you click a "Buy Now" button on an online store and it takes a few seconds for the action to register, that delay is measured as the First Input Delay.  

What Is a Good FID Score? 

A good First Input Delay (FID) score is 100 milliseconds or less. Scores between 100 and 300 milliseconds indicate room for improvement, while delays over 300 milliseconds are seen as poor and negatively affect user experience.
 

First Input Delay (FID) in Detail 

First Input Delay (FID) goes beyond just webpage loading speed. There is more to it. Below, we have highlighted the key insights pertaining to First Input Delay (FID).  

1) What If an Interaction Doesn't Have an Event Listener? 

If an interaction occurs on a webpage without an event listener, the first input won't register as a valid action. This means the user’s click or touch won’t trigger any response, leading to confusion and a poor experience. 

2) Why Only Consider the First Input? 

Only the first input is considered because it reflects the initial user experience (UX). This delay can significantly impact how users perceive the performance of your site. Subsequent interactions are less critical since the first impression sets the tone. 

3) What Counts as a First Input? 

The first input can be any action the user takes, like clicking a button, tapping a link, or pressing a key. It’s essential because it measures how quickly the page responds to user actions, affecting their overall satisfaction. 

4) What If a User Never Interacts With Your Site? 

If a user never interacts with your site, the FID score won't matter to them. However, a high FID can discourage users from engaging in the first place, leading to increased bounce rates and lower overall satisfaction. 

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How to Measure First Input Delay on Your Page?
 

1) Chrome User Experience Report 

The Chrome User Experience Report (CrUX) provides real user data on how visitors experience your site. It collects metrics, including First Input Delay (FID), from users browsing with Chrome. This data helps identify performance issues based on actual interactions. 

2) PageSpeed Insights 

Google's PageSpeed Insights tool analyses your webpage and offers performance metrics, including FID. It provides insights into how quickly the first input is processed, along with suggestions for improving load times and overall user experience (UX). 

3) Google Search Console 

Google Search Console includes the Core Web Vitals report, which features FID as one of its key metrics. This tool gives website owners insights into how their pages perform in real-world conditions, helping identify and address issues that may impact user engagement. 

4) Measure FID in JavaScript 

You can also measure FID directly using JavaScript. By listening for user interactions and capturing the time between the first input and the browser's response, you can get a precise measurement of FID. Implementing this method can help you identify specific areas needing improvement. 

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Differences between the FID and the API 

The common differences between the FID and API are described below: 

1) Purpose 

The purpose of First Input Delay (FID) is to measure the time between a user’s first interaction with a webpage (such as clicking a button or tapping a link) and the moment when the browser begins to process that interaction. FID specifically helps assess the initial responsiveness of the page, providing insight into how quickly a site reacts to user input during the initial loading phase.
 

On the other hand, the Event Timing API serves a broader purpose. It captures comprehensive timing data related to various events, giving a detailed view of different phases of an event’s lifecycle. This makes it valuable for understanding performance bottlenecks across multiple user interactions, rather than just the first one. 

2) Scope 

The scope of First Input Delay (FID) is limited to monitoring the first interaction that a user has with a webpage. It does not take subsequent interactions into account, which means its focus is on the initial load responsiveness and immediate user experience (UX). 

In contrast, the Event Timing API offers a much wider scope by capturing detailed timing information for numerous interactions within a session. This enables developers to gain deeper insights into how various elements on the webpage perform during different stages of user engagement. 

3) Data Collection 

For First Input Delay (FID), data collection relies on real user metrics sourced from the Chrome User Experience Report (CrUX). This means FID reflects the actual performance experienced by users in the wild, making it a robust indicator of a website’s real-world performance. 

Conversely, the Event Timing API provides developers with the ability to gather timing metrics directly from within their own web applications. This flexibility allows for custom measurement of user interactions, enabling more targeted performance analysis that is specific to the application’s context. 

4) User Experience Insight 

First Input Delay (FID) is crucial for understanding the user experience (UX) during the first input. A high FID value indicates delays in interaction processing, which can frustrate users and create a perception of sluggishness, especially during the initial load of the page. 

The Event Timing API, however, provides a more nuanced understanding of performance issues that go beyond the first interaction. By monitoring the timing of multiple interactions, it helps identify specific areas within the webpage that might be causing poor responsiveness, allowing for a more holistic view of the user experience. 

Optimise First Input Delay (FID)  

Optimising First Input Delay (FID) is crucial for enhancing user experience (UX) on your website. Here are some key strategies to improve FID: 

1) Heavy JavaScript Execution 

Heavy JavaScript execution can significantly delay FID. When the browser is busy running scripts, it cannot respond to user interactions. To mitigate this, minimise the amount of JavaScript executed on initial load and consider loading scripts asynchronously.  

2) Break Up Long Tasks 

Long tasks block the main thread and delay user input processing. By breaking up these tasks into smaller chunks, you can ensure the browser remains responsive. This helps users interact with your site more quickly. 

3) Optimise Your Page for Interaction Readiness 

Ensure that your page is optimised for user interaction as soon as it loads. This includes prioritising essential resources and minimising render-blocking elements. A faster page load will lead to quicker interaction readiness. 

4) First-party Script Execution Can Delay Interaction Readiness 

First-party scripts, although necessary, can also impact interaction readiness. Ensure these scripts load efficiently and do not block the main thread, allowing users to interact with the page sooner. 

5) Data-fetching Can Impact Many Aspects of Interaction Readiness 

Data-fetching processes can delay the time it takes for users to interact with your site. Use techniques like lazy loading or on-demand fetching to ensure that data is retrieved without hindering user interactions. 

6) Third-party Script Execution Can Delay Interaction Latency Too 

Third-party scripts, such as ads or social media widgets, can significantly impact FID. Consider deferring these scripts until after the main content is interactive to reduce their impact on load times. 

7) Use a Web Worker 

Web workers allow you to run scripts in the background, freeing up the main thread for user interactions. This can be especially helpful for heavy computations, ensuring that the main thread remains responsive. 

8) Reduce JavaScript Execution Time 

Minimising JavaScript execution time is essential for improving FID. Review your scripts to identify and remove any unnecessary code and use efficient coding practices to reduce the overall execution time. 

9) Defer Unused JavaScript 

If there are scripts that are not needed immediately, defer their loading. This ensures that critical resources are loaded first, improving the initial responsiveness of your site. 

10) Minimise Unused Polyfills 

Unused polyfills can add unnecessary weight to your scripts. Only include polyfills that are essential for your user base, helping to keep the JavaScript bundle size small and enhancing overall performance. 

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Conclusion 

We hope you understand what a First Input Delay (FID) is. Understanding and optimising FID is essential for providing a positive user experience (UX). Businesses can enhance interaction readiness and keep users engaged by measuring FID through various tools and implementing strategies to reduce delays. A focus on efficient script execution and performance optimisation can significantly improve FID scores, ultimately leading to better overall website performance. 

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