FID: definition and replacement by INP
Updated on February 22, 2026
Quick definition
FID (First Input Delay) was a Core Web Vitals metric measuring the delay between a user's first interaction with a page (click, tap) and the moment the browser could begin processing that interaction. FID was replaced by INP (Interaction to Next Paint) in March 2024. FID specifically measured responsiveness to the very first interaction, whereas INP measures responsiveness throughout the entire session.
How it works
FID (First Input Delay) was introduced by Google as a Core Web Vitals metric to measure web page responsiveness. Its principle: capture the delay between a user's first interaction (click on a link, button, form) and the moment the browser actually starts processing that interaction.
This delay existed because the browser's main thread was busy executing JavaScript. FID thresholds were:
- Good: under 100 ms
- Needs improvement: between 100 ms and 300 ms
- Poor: beyond 300 ms
In March 2024, Google officially replaced FID with INP in the Core Web Vitals. This transition reflects FID's limits: it only measured the first interaction, ignored the full processing time and did not faithfully reflect the page's overall interactive experience.
INP, by measuring the worst latency among all interactions in the session, offers a far more complete view of responsiveness.
Why it matters
Even though FID is no longer an official Core Web Vital since March 2024, understanding its history helps grasp the evolution of Google's thinking on page responsiveness.
The optimisations made to improve FID remain entirely valid for improving INP:
- Reducing blocking JavaScript
- Splitting long tasks
- Using web workers
Technical teams that invested in FID optimisation are naturally well positioned to move to INP.
How to improve or use it
Since FID has been replaced by INP, focus your efforts on the latter. The principles remain similar:
- 1Reduce long JavaScript tasks (over 50 ms) by splitting them.
- 2Load third-party scripts asynchronously or deferred.
- 3Use web workers to offload computation from the main thread.
- 4Audit your JavaScript with Chrome DevTools' Performance tab to identify scripts that block the main thread on load.
With Sublim
Sublim lets you track the evolution of your performance metrics over time, including during the FID-to-INP transition. By correlating responsiveness data with actual user behaviour (engagement rate, scroll depth, conversions), Sublim helps you prioritise the optimisations with the most business impact — cookie-free and GDPR-compliant.
Frequently asked questions
When was FID replaced by INP?
Google officially replaced FID with INP (Interaction to Next Paint) as a Core Web Vitals metric in March 2024. The transition had been announced in May 2023 to give developers time to adapt. Since that date, INP is the metric considered in Google rankings.
Why did Google replace FID with INP?
FID had a major limitation: it only measured the delay before the very first interaction, ignoring all subsequent interactions. A page could have an excellent FID but be extremely slow to respond to later clicks. INP measures the latency of all interactions and keeps the worst, providing a far more representative evaluation of overall responsiveness.
Should I still care about FID for my SEO?
No, since March 2024 only INP counts as a Core Web Vitals signal in Google rankings. Google Search Console reports now display INP instead of FID. However, the technical optimisations made for FID (reducing blocking JavaScript) remain beneficial for INP.
Related terms
INP (Interaction to Next Paint) is the [Core Web Vitals](core-web-vita…
Core Web Vitals are a set of three metrics defined by Google to object…
LCP (Largest Contentful Paint) is a [Core Web Vitals](core-web-vitals)…
CLS (Cumulative Layout Shift) is a [Core Web Vitals](core-web-vitals) …