Time to First Byte (TTFB) is the time between the browser requesting a page and receiving the first byte of the response. It includes redirects, DNS lookup, connection and TLS setup, and the time your server takes to respond.
| Rating | TTFB (75th percentile) |
|---|---|
| Good | 0.8 s or less |
| Needs improvement | 0.8 s to 1.8 s |
| Poor | Over 1.8 s |
TTFB is not a Core Web Vital, but every millisecond of it delays FCP and LCP. Caching HTML at a CDN, avoiding redirect chains and speeding up server-side rendering are the usual fixes.