INP in Core Web Vitals: The 2026 Metric
Short answer. Interaction to Next Paint (INP) replaced First Input Delay (FID) as a Core Web Vital in March 2024 and remains the key responsiveness metric in 2026. INP measures the delay between a user interaction and the next frame painted. "Good" is under 200 ms, "needs improvement" is 200–500 ms, and "poor" is over 500 ms. Unlike FID, INP considers every interaction during a session, not just the first one.
Why FID was replaced by INP
FID only measured the delay before processing the first input — the time until the browser began handling the first click or tap. That gave a misleading picture: a page could have an excellent FID yet stutter on every subsequent action. INP closes this gap by evaluating responsiveness across the entire session and reporting the slowest interaction (dropping outliers on long sessions).
INP isn't about load speed — it's about how alive the page feels after it loads. Users don't forgive an interface that thinks longer than they do.
What INP is made of
Each interaction passes through three phases, and INP sums them up:
- Input delay — time while the main thread is busy and can't start handling the event.
- Processing time — execution of the event handlers.
- Presentation delay — time to recalculate styles, run layout and paint the next frame.
INP thresholds
| Rating | INP range | Meaning |
|---|---|---|
| Good | ≤ 200 ms | Responsive UI, the action feels instant |
| Needs improvement | 200–500 ms | Noticeable but tolerable delay |
| Poor | > 500 ms | The interface feels sluggish |
How INP relates to the other Core Web Vitals
In 2026 the Core Web Vitals trio is: LCP < 2.5 s (load speed of the main content), INP < 200 ms (responsiveness) and CLS < 0.1 (visual stability). All three are measured at the 75th percentile of real users. A full breakdown of the trio is in Core Web Vitals 2026: The Complete Guide.
Common causes of poor INP
- Heavy JavaScript in handlers — synchronous computation blocks the main thread.
- Long tasks over 50 ms that prevent the browser from painting a frame.
- Excessive re-renders in SPA frameworks on every keystroke.
- Large DOM — layout recalculation becomes expensive.
- Third-party scripts (analytics, widgets) occupying the main thread.
How to measure INP in practice
INP is a field metric: it's only meaningful when collected from real visitors. Lighthouse in the lab gives an approximation at best. The simplest way to capture INP from real interactions is via PerformanceObserver:
// Collect event-timing to estimate INP in the browser
const observer = new PerformanceObserver((list) => {
for (const entry of list.getEntries()) {
// duration = input delay + processing + presentation
const inp = entry.processingEnd - entry.startTime + entry.duration;
console.log(entry.name, Math.round(inp), 'ms');
}
});
observer.observe({ type: 'event', buffered: true, durationThreshold: 40 });To measure baseline server responsiveness, which affects input delay on first load, curl with formatted timing output is handy:
curl -s -o /dev/null -w "TTFB: %{time_starttransfer}s | total: %{time_total}s\n" https://example.com/What to do to improve INP
Break up long tasks with scheduler.yield() or setTimeout, move heavy computation into Web Workers, use requestIdleCallback for non-critical analytics, minimize DOM size and defer third-party scripts. enterno.io offers RUM monitoring that collects real Web Vitals (including INP) from your visitors — so you spot the problem before it hits your rankings.
FAQ
How is INP different from FID?
FID only measured the delay before the first interaction was processed. INP evaluates every interaction in a session and reports the slowest, giving an honest picture of responsiveness.
What INP value counts as good?
Under 200 ms at the 75th percentile of real users. 200 to 500 ms needs improvement; over 500 ms is poor.
Can I measure INP in Lighthouse?
Lighthouse only gives a lab estimate. Accurate INP comes from field data of real visitors via RUM or CrUX.
Does INP affect SEO?
Yes. Core Web Vitals are a Google ranking factor, and INP has been part of the trio since March 2024.
Check your page's performance right now with the free speed test on enterno.io — it shows Core Web Vitals and points out what's slowing down rendering. The security scanner and HTTP header checker are also useful.