First Input Delay (FID) vs INP
- mohammed jarekji
- 11 minutes ago
- 5 min read
The End of an Era in Web Interactivity Metrics
For years, developers and SEOs measured responsiveness through one key signal: First Input Delay (FID).
It was Google’s way of asking, “How fast does your site respond when users try to interact?”
But as the web evolved into complex, app-like experiences, FID began to fail its own purpose.
A site could “pass” FID and still feel sluggish to users.
So in March 2024, Google officially retired FID, and introduced its smarter, more human successor: Interaction to Next Paint (INP).
“FID was the handshake — INP is the entire conversation.”
What Was First Input Delay (FID)?
FID measured the delay between a user’s first interaction (click, tap, or key press) and the time the browser started processing that event.
In simple terms, it told you how long a user had to wait before the browser acknowledged their input.
FID’s mission was noble — quantify how quickly a page reacts. But it only told part of the story.
Why FID Was Flawed
Despite being a key Core Web Vital for years, FID had several blind spots:
It only measured the first interaction. Everything after — scrolls, clicks, or input sequences — didn’t count.
It ignored visual feedback. Even if input was accepted quickly, users could still be staring at a frozen screen.
It didn’t capture complex app behavior. SPAs (Single-Page Applications) often passed FID while still feeling laggy.
It was overly optimistic. Many sites scored “good” but still caused user frustration.
In other words, FID measured the browser’s reflex, not the user’s experience.
FID told you when your site started listening — not when it actually responded.
Enter Interaction to Next Paint (INP)
To fix those limitations, Google introduced Interaction to Next Paint (INP) — now the official responsiveness metric in Core Web Vitals.
INP measures the entire interaction lifecycle, from input → processing → next visual update.
It captures all interactions, not just the first one, making it a much better reflection of real-world responsiveness.
Where FID stopped at the starting line, INP watches the whole race.
FID vs INP — The Complete Comparison
FID measured how fast the site reacts. INP measures how smoothly it interacts.
Why Google Replaced FID
FID wasn’t wrong — it was simply outgrown.
As the modern web embraced React, Angular, and dynamic content, Google realized that FID’s simplicity couldn’t keep up.
Internal studies from the Chrome UX Report (CrUX) revealed a weak correlation between FID scores and perceived responsiveness.
Developers were optimizing for the metric, not the experience.
INP bridges that gap — it aligns performance data with what humans actually feel.
How FID Worked (and Why It Fell Short)
When a user clicked something, FID tracked how long the browser was blocked from handling that event — often due to long JavaScript tasks. But even after that initial delay, the browser could still be busy rendering, calculating, or animating — which FID ignored.
Imagine pressing an elevator button that lights up instantly (good FID), but the elevator doesn’t arrive for 10 seconds (bad INP).
That’s why Google evolved.
How to Transition from FID to INP Optimization
Since FID is no longer measured, your optimization focus should shift to the entire interaction lifecycle.
1. Audit JavaScript Execution
Split long tasks using requestIdleCallback() or Web Workers.
Minimize main-thread blocking.
Use async and defer attributes for non-critical scripts.
2. Reduce Layout Thrashing
Avoid frequent DOM recalculations.
Batch style reads and writes.
3. Use Optimistic UI Updates
Show visual feedback (e.g., button animation) before the final action completes. This creates perceived responsiveness even during small delays.
4. Lazy Load Non-Essentials
Analytics, widgets, and chat scripts should load after the main interactivity milestone.
5. Test Responsiveness Holistically
Use:
Lighthouse v11+
PageSpeed Insights (INP section)
Chrome DevTools Performance Tab
The End of FID — A Historical Milestone
FID’s life cycle was short but meaningful:
2020: Introduced as one of the first Core Web Vitals.
2024: Officially deprecated, replaced by INP.
Its contribution? It made developers care about responsiveness as much as speed and stability. Now, INP carries that torch — more sophisticated, inclusive, and user-centric.
FID and EEAT — Why Responsiveness Still Matters
Even though FID is gone, its principle lives on in Google’s broader vision for EEAT (Experience, Expertise, Authoritativeness, Trustworthiness).
A responsive website enhances Experience and Trust.
When a site reacts instantly, users subconsciously perceive it as competent and credible.
Fast feedback loops = psychological trust = SEO edge.
Final Takeaway
FID walked so INP could run.
FID taught us the value of fast feedback, but INP brings us closer to what users actually experience.
As Google refines its metrics, the lesson is clear: Stop chasing scores — start crafting sensations.
“From speed to sensitivity — optimize for what users feel, not just what tools measure.”
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FAQs
When did Google officially deprecate First Input Delay (FID)?
Google officially deprecated First Input Delay (FID) in March 2024 and replaced it with Interaction to Next Paint (INP) as the primary responsiveness metric in Core Web Vitals. INP now measures the full interaction lifecycle instead of just the first input delay.
Why did Google replace FID with INP?
FID only measured the delay before the first interaction was processed, which often failed to represent real-world responsiveness. INP provides a more complete picture by tracking the time from user input to the next visual update across all interactions. It reflects the actual smoothness and usability of a page.
How do I optimize my site for INP instead of FID?
To optimize for INP, focus on reducing main-thread blocking and improving interaction feedback. Break long JavaScript tasks into smaller chunks, use async or defer for non-critical scripts, preload critical resources, and implement optimistic UI updates. Use Lighthouse v11+ or PageSpeed Insights to measure INP performance directly.
Does FID still appear in Search Console or reports?
No. As of 2024, FID has been fully removed from Core Web Vitals reports in Search Console and replaced by INP. Historical FID data may still appear in archived reports, but Google now evaluates responsiveness solely through INP metrics in both lab and field data.
How does the transition from FID to INP affect SEO rankings?
While the overall impact on rankings is moderate, INP has a stronger connection to perceived responsiveness and user satisfaction. Sites that maintain low INP scores (under 200 ms) tend to provide better user experiences, which can indirectly improve engagement, dwell time, and search performance over time.
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