TTI (Time to Interactive) is a lab metric that measures when a page becomes fully interactive. A page is considered interactive when it displays useful content, event handlers are registered, and the main thread is idle enough to respond to user input within 50 milliseconds.
How TTI Works
TTI looks for a "quiet window" after First Contentful Paint. This quiet window is a 5-second period where no long tasks (over 50ms) execute and no more than two in-flight network requests exist. TTI marks the end of the last long task before this quiet window.
The metric captures when users can start interacting with page elements without experiencing delays or unresponsive behavior.
TTI Thresholds
General thresholds for TTI scores:
- Good: Under 3.8 seconds
- Needs Improvement: Between 3.8 and 7.3 seconds
- Poor: Over 7.3 seconds
E-commerce sites typically aim for TTI under 3 seconds on mobile devices.
Current Status
TTI was removed from Lighthouse 10 due to high variability. The metric proved overly sensitive to outlier network requests and long tasks, producing inconsistent results across measurements.
Newer metrics like INP, TBT, and LCP now provide better indicators of page interactivity and load performance. TBT in particular serves as a more stable lab-based alternative for measuring thread blocking.
When TTI Still Matters
Despite deprecation from Lighthouse, TTI remains useful for understanding the overall loading experience. Some monitoring tools still report it, and the concept of "time until reliably interactive" helps frame performance conversations with stakeholders.
