TTFB (Time to First Byte) is a performance metric measuring the time from request initiation to the arrival of the first byte of the response, indicating server and network responsiveness.
TTFB is not a Core Web Vital but it strongly influences LCP — a 500ms TTFB caps LCP at 500ms+ no matter how fast the page renders after. 2026 thresholds (informal): ≤ 800ms good, ≤ 1.8s needs improvement, > 1.8s poor.
TTFB components: DNS resolution, TCP/TLS handshake, server processing time, and network transit from server to client. Edge rendering (Vercel, Cloudflare Workers, Netlify Edge) drives TTFB to the 30–100ms range from typical user locations. Monolithic origin-rendered applications (most PHP-based ecommerce) commonly land at 300ms–2s TTFB depending on cache state.
For ecommerce, low TTFB compounds: it pulls LCP down, makes pagination feel instant, and reduces the perceived latency of every navigation. Cache Components + PPR in Next.js 16 makes edge-tier TTFB the default for catalog pages.