What is time-to-interactive (TTI)?

Time to Interactive (TTI) is a metric that shows how many milliseconds after the page loads the user can start fully interacting with it (clicking buttons, entering text, and so on), with the site responding quickly.

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#What counts as interactivity

• interface elements are already painted
• JavaScript has finished running heavy tasks
• there are no long blocking processes on the main thread
• the site responds to clicks and input without noticeable delay

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#Example

The page loaded visually in 1.5 seconds, but scripts block interaction for another 3 seconds. In that case, TTI would be about 4.5 seconds. The user sees the page but cannot do anything with it, which is bad UX.

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#Why this matters

• TTI affects how "alive" the site feels
• a long TTI causes frustration: "the site is there, but nothing works"
• TTI is factored into Google Lighthouse and affects SEO through Core Web Vitals

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#Conclusion

TTI is not about "when the site looks ready", it's about "when it actually starts working".