Interaction to Next Paint (INP)

What INP measures

Interaction to Next Paint measures the delay between someone interacting with your page — a tap, a click, a key press — and the screen visibly updating in response.

It watches every interaction across the whole visit and reports a value representing the page’s overall responsiveness, rather than picking the single worst outlier. That makes it a fair reflection of what using the page feels like, not just how it behaved once.

Thresholds

• Good: 200 milliseconds or less
• Needs improvement: 200 to 500 milliseconds
• Poor: over 500 milliseconds

Measured at the 75th percentile of real visits.

Why it replaced First Input Delay

FID only measured how long the browser took to begin handling the first interaction. It did not measure how long the work took, and it ignored every interaction after the first. Nearly every site passed it, which made it a poor signal.

INP became a stable Core Web Vital in 2024 and FID was retired. The practical consequence is that sites which comfortably passed the old metric can fail the new one — nothing about them changed except that the measurement got honest.

What makes a page feel slow to touch

Responsiveness problems are almost always about the browser’s main thread being busy. It can only do one thing at a time, and while it is occupied your tap simply waits:

• Heavy third-party scripts. Chat widgets, review carousels, heat-map trackers, and tag managers each add work on every interaction.
• Expensive event handlers. Code that recalculates far more than it needs to on every click or scroll.
• Large DOM trees. Page builders routinely produce thousands of nested elements; every layout recalculation gets more expensive as that grows.
• Work done at the wrong time. Analytics and non-urgent updates run synchronously inside the click handler instead of after the screen has updated.

The one that surprises people

INP counts the time until the next paint — until something visibly changes. A page can process a tap almost instantly and still score badly if it does not show any acknowledgement.

This makes some INP fixes a design problem rather than a performance problem. Showing an immediate loading state on a form submit, or a pressed state on a button, both improves the score and makes the page feel better, without making the underlying work any faster.

Mobile is where this gets decided

Phones have far less processing power than the laptop your site was built on, and Core Web Vitals are graded separately for mobile. A page that feels instant on a developer’s machine can sit well past 500 ms on a three-year-old Android — and for most local businesses, that phone is the majority of the traffic.