Core Web Vitals: What is First Input Delay?

In one of our recent posts, we discussed how Google will measure your website’s performance based on a new set of factors called core web vitals.

Core web vitals has three specific measurements: First Input Delay, Largest Contentful Paint and Cumulative Layout Shift.

Let’s talk about First Input Delay in more detail.

What is First Input Delay?

How long does a user have to wait for the site to respond after he has clicked on a link or tapped a button?

This wait time is what’s called FID or First Input Delay.

FID tracks the input delay between when a user first interacts with a site with a definite action (such as clicking a button or link, not scrolling or zooming a page) and when that site becomes interactive.

You can think of FID as the time it takes for someone to get to the door after ringing their doorbell.

Why is a short FID important?

Users don’t like waiting. To provide them a good experience and leave a great first impression, it’s fundamental to make the wait as short as possible.

But FID doesn’t just measure the quality of user experience when he visits a site or page, Google will also use it when ranking sites.

The shorter the input delay, the better.

How long (or short) should the First Input Delay be?

Ideally, your page should have an FID of 100 milliseconds or less. At this score, users will feel your site is instantaneous.

Scores from 100 to 300ms should be improved.

Scores that are over 300ms are considered poor.

75% of the total page loads for both desktop and mobile devices is a good threshold to remember. This will ensure you are hitting the target for most users.

However, Google highly recommends aiming for a score of 95 to 99% of page loads.

How is FID measured?

Although testing in the lab is a good enough way to measure site performance, it doesn’t necessarily reflect how real users experience your site.

FID is the only metric which can’t be measured with lab tools. It requires real users to actually interact with your website.

Once real world data has been collected, you can check your FID results in Pagespeed Insights or Search Console

What you can do to optimise your site for a better FID

For a better FID score, you can try these:

  • Minify unused Javascript
  • Optimise your CSS code
  • Avoid or postpone long-running Javascript
  • Defer the loading of third-party code
  • Utilise web workers
  • Long tasks should be broken down into smaller tasks

If you need some help optimising your site for a better FID score, head over to and get a conversion audit.