Break time to first byte into network and server components.
TTFB gates every other loading metric, so improving it shifts the entire waterfall earlier. A CDN reduces connection overhead by terminating close to the user but does nothing for server processing. Because every downstream metric inherits TTFB, it is usually the highest-leverage single optimisation on a slow site.
Time to First Byte
TTFB = DNS + TCP + TLS + server processing + response transfer
TTFB = DNS + TCP + TLS + server processing + response transfer TTFB gates every other loading metric, so improving it shifts the entire waterfall earlier. A CDN reduces connection overhead by terminating close to the user but does nothing for server processing.
Because every downstream metric inherits TTFB, it is usually the highest-leverage single optimisation on a slow site.
This calculator takes 5 inputs: DNS lookup, TCP connection, TLS negotiation, Server processing, Response transfer. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.