How does TTFB differ from server response time?

TTFB is counted from the start of navigation and includes redirects, DNS and secure connection, while server response time measures only the gap between sending the request and the first byte arriving. The second number is always smaller and the thresholds defined for the first do not apply to it; for troubleshooting, that split is what tells you whether to talk to the network team or the backend team.

Time to First Byte (TTFB)

Intermediate

Updated Jul 11, 2026 Shahin editorial 2 min read

PronunciationEN/taɪm tə fɜːrst baɪt/

Time to First Byte, or TTFB, is the interval between the start of navigation and the arrival of the first byte of the server's response in the browser.

Contrary to a common assumption, the value is not just the server's thinking time. By the standard definition it covers redirects, service worker startup, DNS lookup, connection and TLS setup, sending the request and finally waiting for the server, so a bad TTFB can be a network problem with no fault in the backend. There is also a tool-to-tool mismatch here: many monitoring products label only the server wait as TTFB, and that figure is not comparable with the standard one. TTFB is not a Core Web Vital and its role is diagnostic, because nothing can be painted before the first byte arrives, so a high TTFB is usually the first explanation for a poor LCP.

How it is calculated

Time to first byte = the moment the first byte of the response arrives minus the moment navigation started

The interval includes redirects, DNS lookup, connection and TLS setup, sending the request and the server wait, so it is not the same as server response time, which measures only the wait, and the quality bands of one are not valid for the other. The unit is milliseconds and the reported figure should be a percentile rather than an average; per web.dev, under 800 milliseconds is good and above 1800 milliseconds is poor.

FAQ

Sources:web.dev — Time to First Byte (TTFB)MDN — PerformanceNavigationTiming