What Is INP?
INP (Interaction to Next Paint) measures the delay between a user's interaction with a page (a click, keystroke, or touch) and the moment the browser renders the next frame reflecting that update.
Thresholds:
- Good: < 200ms
- Needs Improvement: 200-500ms
- Poor: > 500ms
How INP Differs from FID
| Metric | What It Measures | How It's Calculated |
|---|---|---|
| FID (deprecated) | First-interaction delay | Takes the first interaction |
| INP (new metric) | Full-session interaction delay | Takes the 98th percentile across all interactions |
INP is stricter: it doesn't just look at the first click—it monitors the response latency of every interaction the user makes throughout their entire visit.
Common INP Problems and How to Fix Them
Problem 1: Long Tasks blocking the main thread
- Cause: Large JavaScript execution blocks that can't be interrupted
- Fix: Break long tasks into multiple smaller tasks
Problem 2: Framework rendering performance issues
- Cause: Frameworks like React/Vue trigger heavy re-renders on state updates
- Fix: Use optimization hooks such as useMemo and useCallback
How to Measure INP
- Lab measurement: The Performance panel in Chrome DevTools, or Lighthouse
- Real-user data: The Core Web Vitals report in Google Search Console (recommended)
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