Glossary
What is Time to Interactive (TTI)?
Time to Interactive (TTI) was removed from Lighthouse 10 in February 2023. Use TBT for lab measurement and INP for field measurement.
Time to Interactive measured when a page became fully interactive - displaying useful content, event handlers registered, and responding within 50ms. It identified a 5-second "quiet window" with no Long Tasks.
Why TTI Was Deprecated
Google removed TTI because:
- Overly sensitive to outliers - A single late network request could dramatically inflate TTI
- Better alternatives exist - TBT measures blocking more robustly
- Poor correlation with real experience - Terrible TTI could still feel responsive
What Replaced TTI
Lab Testing
Total Blocking Time (TBT) - Measures cumulative main thread blocking. Now has 30% Lighthouse weight.
Field Measurement
Interaction to Next Paint (INP) - Measures actual interaction responsiveness. Core Web Vital since March 2024.
Historical Thresholds
| Score | Rating |
|---|---|
| ≤ 3.8s | Good |
| 3.8s - 7.3s | Needs Improvement |
| > 7.3s | Poor |
Migration
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