What Is First Input Delay (FID)?

First Input Delay (FID) is a metric used to measure the responsiveness of a website. It is the time in milliseconds between when a user first interacts with a webpage and when the browser can respond to that interaction.

FID is a crucial metric for web designers and an integral part of understanding your website performance. It reflects the user's perception of the website's loading speed and responsiveness to their interactions, a core aspect of the user experience. Impacting the user experience, FID is a critical part of SEO; it is one of the Core Web Vitals metrics. Web designers must understand the impact of FID on user experience and conversion rates and optimize the website's performance to minimize FID and improve the overall user experience.

To improve your website's performance and the resulting user experience, it is important to understand the impact FID can have on your marketing efforts and website performance.

  • A high FID can lead to a poor user experience, negatively impacting engagement and conversion rates. Users may become frustrated with slow-loading pages and leave your website before they even have a chance to explore what you offer. This can lead to lost revenue and a decrease in customer satisfaction.
  • On the other hand, a low FID can help ensure that users have a positive experience on your website, leading to increased engagement, conversion rates, and, ultimately, revenue. A website that loads quickly and responds to user input promptly is more likely to keep visitors engaged and encourage them to explore your products and services.


So, what can you do to improve your website's FID and user experience? Here are a few tips:

  • Minimize the amount of code and resources needed to load a page: This can be achieved by removing unnecessary code, optimizing images and videos, and using a Content Delivery Network (CDN) to deliver content to users quickly.

  • Implement lazy loading: Lazy loading allows you to load only the resources needed for the user to see and interact with the page rather than loading all resources simultaneously. This can significantly improve FID and page load times.

  • Use a performance budget: A performance budget limits the resources and code used on a page, which can help you identify and eliminate unnecessary resources causing delays.

  • Optimize your JavaScript: Use techniques like code splitting, tree shaking, and minification to reduce the amount of JavaScript that needs to be loaded and executed.

  • Use browser caching: Browser caching allows a user's browser to store resources locally, so they don't have to be downloaded again on subsequent visits to the website, which can significantly improve FID.

  • Use a Performance monitoring tool: Use tools like Google Lighthouse or webpagetest.org to measure your website's performance and identify areas for improvement.

  • Consider implementing progressive web apps, which can load quickly and work offline.

By implementing these techniques, you can significantly improve FID and provide a better user experience for your website visitors.