Definition
Time to Interactive (TTI) measures the time elapsed between the start of page loading and when the page is fully interactive, meaning it can reliably respond to user interactions within 50ms. TTI is reached when useful content is visible (FCP reached), event handlers are registered, and the page responds to interactions within acceptable delay. This metric has become less central since INP's introduction in Core Web Vitals, but remains valuable for performance audits. A TTI above 7.3 seconds is considered poor by Lighthouse.
Key Points
- Measures when the page is fully interactive and responsive to user actions
- Recommended threshold: below 3.8s (good), above 7.3s (poor)
- Less central since INP, but still relevant for audits
Practical Examples
Heavy JavaScript page
A React SPA displays content in 1.5s (FCP) but isn't truly interactive until 8s (TTI) due to hydration and bulky JavaScript bundles.
Progressive optimization
Implementing server-side rendering and lazy loading of non-critical components reduces an e-commerce site's TTI from 9.2s to 3.8s.
Frequently Asked Questions
No, TTI has never officially been part of Core Web Vitals. INP replaced it as the reference interactivity metric. However, TTI remains in Lighthouse and useful for technical audits.
A large gap between FCP and TTI indicates the page displays content quickly but remains blocked by JavaScript. The solution involves JavaScript optimization (code-splitting, defer, lazy loading).
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Last updated: 2026-02-07