First Input Delay (FID)
A metric measuring the delay between a user first interaction and the browser response.
Why It Matters
FID indicates whether your page feels responsive when users try to interact with it.
How It Works
FID measures the time from when a user first clicks a link, taps a button, or uses a form control to when the browser begins processing that event. Good FID is under 100 milliseconds.
Real-World Example
A page with heavy JavaScript has 350ms FID; code splitting reduces it to 80ms.
Common Mistakes
Ignoring FID because lab tools cannot measure it
Loading too much JavaScript on initial page load
Related Terms
A Core Web Vital measuring how quickly a page responds visually to user interactions.
A set of Google metrics measuring page loading speed, interactivity, and visual stability.
A Core Web Vital measuring how long it takes for the largest visible element to load.
First Input Delay (FID) FAQs
Is FID still used by Google?
Google replaced FID with Interaction to Next Paint (INP) as a Core Web Vital in March 2024.
How do I improve FID?
Reduce JavaScript execution time, break up long tasks, and use web workers for heavy processing.
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