You can optimise images and defer scripts all day, but nothing renders until the first byte arrives. If the server takes 1.2 seconds to respond, every visitor starts 1.2 seconds behind.
What TTFB includes
Time to First Byte is the gap between the browser asking for a page and the first byte of the response coming back. Inside that window: the DNS lookup, the connection and TLS handshake, the request travelling to the server, the server building the page, and the response starting its trip back.
Your host influences most of it: how fast it builds the page, whether the page is cached, how well its network is connected, and how far it is from the visitor.
Directional. Caching and proximity are the two big levers.
How it feeds Core Web Vitals
One of the Core Web Vitals, Largest Contentful Paint, measures the time until the main content appears. It cannot even begin until the HTML arrives, so a high TTFB is added straight onto it. Google's guidance puts a good TTFB under 800 ms; to give LCP room to pass, aim well below that, somewhere around 200 to 400 ms.
Interaction to Next Paint, the responsiveness metric, is less about TTFB, but a server that is slow under load often also blocks on slow database queries, which shows up as janky interactions.
Bringing it down
- Cache the page. A server-side page cache turns a 700 ms build into a 100 to 150 ms lookup. Biggest single win.
- Add a CDN with full-page caching. Now the response comes from a location near the visitor, often under 60 ms.
- Host near your audience. If most visitors are in one country, a server there removes hundreds of milliseconds of travel for the uncached requests.
- Fix slow queries and heavy plugins. For logged-in pages that cannot be cached, the build time is the number, so profile it.
- Use current PHP and enough resources. PHP 8.2 or newer is meaningfully faster, and a starved plan builds pages slowly.
Measure the right thing. A lab tool tests from one location. Real users are everywhere. Check field data in Search Console's Core Web Vitals report and in the Chrome UX data inside PageSpeed Insights, and look at your slowest region, not just the average.
What to ask a host
- Server-side page caching, named (LSCache, NGINX cache, Varnish)
- A free CDN, or clean support for putting one in front
- Data centre locations that match where your visitors are
- Current PHP, with OPcache on
- Redis or Memcached for the pages that cannot be page-cached
MD Saiful Islam · Founder & Head of SEO
When a client's Core Web Vitals will not pass, the first thing we check is TTFB in the field data. If it is over a second, no amount of front-end work will fix the score. Cache the pages and, if needed, move the host closer to the audience, then re-measure.
Illustrative example
Clean front end, stuck score
Images compressed, scripts deferred, and LCP still would not pass. The field data told the story: TTFB near 1.1 seconds, because the shared host rebuilt every page from scratch on every request.
Switching on the page cache and a CDN took field TTFB to about 250 ms. LCP moved into the green with no change to the theme at all.