What Is INP?
INP measures how quickly a page responds after a user interacts with it. Why it replaced FID, common causes, and a real example.
INP (Interaction to Next Paint) is a Core Web Vitals metric that measures how quickly a page responds after a visitor interacts with it, such as clicking a button or tapping a menu. It replaced First Input Delay (FID) as the official responsiveness metric in March 2024, and remains the standard in 2026.
Why INP matters
INP replaced the older First Input Delay metric because it captures responsiveness across every interaction on a page, not just the first one, and reports the worst interaction rather than an average, a much more representative picture of real frustration. Pages with heavy JavaScript execution often score poorly here, making visitors feel like clicks aren’t registering, exactly the kind of experience that quietly drives people away without them consciously realizing why the site feels sluggish. INP is widely reported as the Core Web Vital most sites currently fail, and the hardest of the three to fix, since it requires architectural changes to how JavaScript executes rather than a simple asset optimization.
What causes poor INP
- Long JavaScript tasks. Any task running over 50 milliseconds blocks the main thread, delaying the browser’s ability to respond to input.
- Heavy third-party scripts. Ad networks, analytics, and chat widgets often run expensive JavaScript that competes with your own code for the main thread.
- Excessive DOM size. A very large, complex page structure makes every interaction more expensive to process and repaint.
- Unoptimized event handlers. Poorly written click or input handlers that do more work than necessary before the next paint.
How to improve INP
- Break up long JavaScript tasks into smaller chunks that yield back to the main thread regularly.
- Defer non-critical JavaScript so it doesn’t compete with interaction handling during initial load.
- Audit and reduce third-party scripts, each one is a potential source of unpredictable main-thread blocking you don’t directly control.
- Simplify overly complex DOM structures where possible, particularly on pages with heavy component nesting.
- Use Chrome DevTools’ Performance tab to record real interaction sessions and identify the specific tasks causing delay.
INP thresholds
| Score | Threshold |
|---|---|
| Good | Under 200 milliseconds |
| Needs improvement | 200 to 500 milliseconds |
| Poor | Over 500 milliseconds |
Real example
For example, if a visitor clicks “Add to Cart” and the button visibly updates 400 milliseconds later, that delay is measured as part of the page’s INP, landing in the “needs improvement” range, likely caused by heavy JavaScript running on the main thread at the moment of the click.
INP and AI search
INP has no direct bearing on AI Overview citation, but a visitor arriving from an AI-cited link who experiences unresponsive buttons or laggy interactions is more likely to abandon the page quickly, undermining the value of that citation regardless of how well the content itself was written.
FAQ
Why did INP replace FID?
FID only measured the delay before the browser started processing the first interaction. INP measures the full time from interaction to visual update, across every interaction on the page, a far more complete picture of real responsiveness.
Why is INP the hardest Core Web Vital to fix?
Unlike LCP or CLS, which usually have straightforward asset-level fixes, INP problems stem from JavaScript execution patterns, requiring genuine code architecture changes rather than a simple compression or attribute fix.
Do third-party scripts affect my INP score?
Yes, significantly. Ad networks, chat widgets, and analytics scripts you don’t control can consume main-thread time and directly worsen your site’s measured responsiveness.
Does INP only measure clicks?
No, it covers clicks, taps, and key presses, essentially any discrete user interaction, and reports the worst-performing interaction observed during the page visit.
Related terms
If your Core Web Vitals report shows one metric consistently in the red, it’s probably INP. It’s the hardest to fix and the easiest to ignore, don’t.