FID: What Is First Input Delay and How to Optimize This Core Web Vitals Metric

First Input Delay (FID)

First Input Delay (FID), also known as the “delay before interaction,” measures the time between a user’s first interaction with a webpage (e.g., clicking a link, tapping a button, or using a JavaScript-based custom control) and the browser’s actual response to that interaction. This metric is crucial for assessing user experience during initial page engagement and is one of the Google Core Web Vital Metrics.

Technically, FID quantifies the time in milliseconds from a user’s first action on a webpage to the browser’s response to that action. It excludes time spent on scrolling or zooming.

How to Measure First Input Delay

FID is measured based on the first interactive action performed by a user and is particularly relevant for pages where user interaction is necessary.

A low FID score indicates better usability, whereas a high FID score signifies a less satisfying user experience. The time between rendering content and achieving full interactivity varies significantly depending on:

• The size and complexity of JavaScript that needs to be downloaded, processed, and executed.
• The device’s speed, particularly with low-end mobile devices.

To minimize site initialization time and reduce input delays, it is essential to optimize the webpage and streamline resource-heavy operations.

Key Points:

• FID is a field-measurable metric requiring real user interaction and cannot be tested in a lab environment.
• However, Total Blocking Time (TBT), a lab-measurable metric, closely correlates with FID and captures interactivity-impacting issues. Optimizing TBT can also improve FID.

Tools for Measuring FID:

1. PageSpeed Insights
2. Web-Vitals JavaScript Library
3. Chrome User Experience Report (CrUX)
4. Google Search Console

Analyzing the distribution of FID values is critical. While the 75th percentile is commonly used for Core Web Vitals, Google recommends also considering the 95th and 99th percentiles for FID to identify areas needing urgent improvement.

Optimal FID Values

To meet the Core Web Vitals standards for First Input Delay, the 75th percentile of recorded page loads must stay below 100 milliseconds. Specifically:

• Good FID: ≤ 100ms
• Needs Improvement: 100ms to 300ms
• Poor INP: > 300ms

How to Optimize First Input Delay

To reduce FID and improve page interactivity, consider the following strategies:

• Minimize Third-Party Code Impact
  – Limit external scripts that add significant delays.

• Reduce JavaScript Execution Time
  – Use techniques like tree-shaking to remove unused code.
  – Implement code splitting to load only necessary parts of JavaScript.

• Lighten the Main Thread
  – Free the main thread by deferring non-critical tasks and optimizing code execution.

• Optimize Resource Requests

  • Minimize the number and size of data requests.
  • Prioritize critical resources for faster load times.

• Break Down Long Tasks
  – Split lengthy tasks into smaller, asynchronous chunks.

• Use Web Workers
  – Execute JavaScript on a separate thread to prevent blocking the main thread.

Google’s Transition from FID to INP

Starting March 2024, Google replaced FID with Interaction to Next Paint (INP) as the Core Web Vitals responsiveness metric. INP evaluates a page’s overall responsiveness by considering all interactions on the page and reporting a single value representing responsiveness.

SEOs have focused heavily on FID as part of Core Web Vitals optimization. With the shift to INP, efforts must pivot to understanding and improving this new metric.

Google Search Console integrated INP into Core Web Vitals reporting and FID was fully replaced.

Explore our detailed guide on optimizing INP for actionable insights.

Simplifying FID Optimization with Tuurbo

Optimizing Core Web Vitals, including FID, often requires significant technical expertise and depends on a site’s structure, such as its CMS. To streamline this process, Tuurbo automates these optimizations, improving Core Web Vitals within 48 hours - no lengthy development cycles or costly consultations needed.

Discover how Tuurbo can elevate your site’s performance effortlessly.

Does it seem like magic?

You don’t believe it, do you?! Try it!

Try our solution, enjoy the results, and decide how long to keep your subscription active.