What is Time to First Byte (TTFB)?
Time to First Byte (TTFB) is the amount of time a browser waits after requesting a page before it receives the first byte of the server's response. It's an early-stage performance measure that happens before any rendering begins, making it a useful diagnostic for server and network issues separate from front-end page weight.
TL;DR
TTFB is how long a browser waits for the server to send back its very first byte, and because it happens before rendering starts, it's the earliest possible signal of a server or network slowdown.
Formula
TTFB = Timestamp of First Response Byte Received - Timestamp of Request Sent
Why It Matters
TTFB matters because it sits at the front of the entire page load timeline, so a slow TTFB delays every other loading and rendering metric that comes after it, no matter how optimized the front-end code is. That makes it the first thing worth checking when overall load time degrades without any recent front-end changes, since it isolates whether the problem is server-side or client-side. It's especially sensitive to backend issues like slow database queries, overloaded servers, or under-provisioned hosting during traffic spikes. Because search engines factor page speed into ranking and user experience signals, a chronically slow TTFB can quietly suppress a site's performance even when the actual page content and design are solid. Monitoring it separately from full page load time helps teams diagnose problems at the right layer instead of guessing.
Example
A page's TTFB jumps from a typical 180 milliseconds to over 900 milliseconds after a traffic spike overwhelms the server's database queries. Because TTFB happens before the browser can even start downloading or rendering the page's actual content, a slow TTFB delays every single other loading metric that comes after it, which is why it's usually the first thing checked when a page's overall load time degrades without any front-end code changes.
Frequently Asked Questions