What is INP (Interaction to Next Paint), the metric that replaced FID

INP (Interaction to Next Paint) is the Core Web Vitals metric for responsiveness: how long the site takes to react visually after each click, tap or key press. In March 2024 it replaced the old FID (First Input Delay) as the official metric.

Why INP replaced FID

FID measured only the delay of the first click and ignored what happened afterwards. INP evaluates virtually every interaction during the visit and counts the full time until the screen responds — a far more honest picture of how snappy or sluggish the site feels.

What is a good INP?

Measured at the 75th percentile of visits, in milliseconds:

• Good: up to 200 ms.
• Needs improvement: between 200 and 500 ms.
• Poor: above 500 ms.

What worsens INP

• Heavy JavaScript that holds the main thread and delays the response to a click.
• Long tasks that block the browser for more than 50 ms.
• Too many third-party scripts — chats, pixels, A/B tests — competing for the CPU.
• Expensive re-renders on every interaction in poorly optimized interfaces.

How to improve INP

• Break long tasks into smaller chunks and yield control back to the browser between them.
• Defer or remove non-essential JavaScript and load third-party scripts at low priority.
• Give immediate visual feedback on the click before processing the heavy work.
• Optimize rendering: avoid recomputing the whole screen on every interaction.

Responsiveness is the difference between a site that feels like an app and one that feels stuck. A high INP breaks the perception of quality at the exact moment the visitor decided to act — click buy, submit, move forward.

How to measure your site's INP

First Class Dev's Speed X-Ray uses Google's official field data (Core Web Vitals) to show where your site stands on each metric, INP included, and what to prioritize.