TTFB & Latency Impact Simulator
See what dropping your Time to First Byte from a sluggish 1,200ms down to an edge-cached 200ms is actually worth — in conversion rate and in dollars, not just milliseconds.
Time to First Byte is the clock that starts every other loading milestone on your page — nothing can render until the first byte arrives, no matter how optimized your images or CSS are. Server performance experts talk about TTFB in milliseconds; this simulator translates those milliseconds into what actually matters to a business: conversion rate and revenue, using published research on how site speed affects buyer behavior.
Enter your current and target TTFB, plus your traffic and conversion numbers. Not sure of your TTFB? Check it free in Chrome DevTools’ Network tab (the “Waiting (TTFB)” value) or at webpagetest.org.
If you’re writing about site speed, Core Web Vitals, or hosting performance, here’s a ready-to-paste link to this simulator.
How this simulator works
Published research on page speed and conversion (from Google, Deloitte, Akamai, and various conversion-rate studies) consistently shows conversion rate improving as latency drops, with the exact sensitivity varying by industry — ecommerce and travel tend to be highly speed-sensitive, while lead-generation and B2B sites are somewhat less so. Rather than extending that relationship in a straight line forever — which would predict absurd results for very large improvements — this simulator applies a diminishing-returns curve: your first 100ms of improvement delivers close to the full researched lift, while later milliseconds add progressively less, capped at a realistic ceiling.
Largest Contentful Paint (LCP) — a Google Core Web Vital and confirmed ranking signal — starts counting only after the first byte arrives. A slow TTFB doesn’t just feel sluggish; it mechanically delays LCP, First Contentful Paint, and every rendering milestone that follows it, by exactly the amount of time TTFB itself takes.
Going from 800ms to 700ms and going from 300ms to 200ms are not equally valuable, even though both are 100ms improvements. This simulator’s curve reflects that the first chunk of improvement typically matters most, rather than assuming every millisecond is worth exactly the same amount forever.
There are two distinct ways to cut TTFB: serve cached responses from a CDN edge location near the visitor so the request never reaches your origin server at all, or make the origin server itself faster (better hosting, object caching, optimized database queries). The two are complementary — edge caching helps cacheable pages; a faster origin helps everything else, including logged-in and dynamic requests that can never be cached.
Reading your results
The modeled relative increase in your conversion rate from the TTFB improvement you entered, using your industry’s typical speed sensitivity and this simulator’s diminishing-returns curve. Treat it as a planning estimate, not a guarantee — the only way to know your site’s actual sensitivity is a real A/B test.
Your current traffic and average order or lead value, applied to the extra conversions the modeled lift would produce. This is the number worth bringing to a hosting or infrastructure budget conversation — it reframes a hosting upgrade as a revenue decision rather than a pure cost.
Frequently asked questions
Time to First Byte is the time between a browser requesting a page and receiving the first byte of the response — it captures DNS lookup, connection setup, server processing, and network latency, before any actual page content starts arriving. It matters for conversions because visitors perceive the entire wait as “the site is slow,” and a growing body of research links slower page speed to lower conversion rates across nearly every industry that’s been studied.
TTFB itself is not one of the three official Core Web Vitals (LCP, INP, and CLS), but it directly gates Largest Contentful Paint, which is a Core Web Vital and a confirmed ranking signal. Google’s own developer documentation lists TTFB as a key diagnostic specifically because a slow TTFB makes a good LCP score very difficult to achieve, whatever else you optimize.
Google’s published guidance treats a TTFB of 800ms or less as “good,” anything above 800ms up to 1,800ms as “needs improvement,” and anything over 1,800ms as “poor.” Sites relying purely on origin server performance often land in the 600–1200ms range; edge-cached responses commonly land under 250ms.
TTFB is only the first leg of the journey — it ends the moment the first byte arrives. Total page load time also includes downloading and rendering every image, script, and stylesheet, and executing any JavaScript that runs on load. A page can have an excellent TTFB and still load slowly overall due to heavy, unoptimized front-end assets — the two are related but solved with different techniques.
The biggest levers are: a CDN or edge cache serving responses from a location near the visitor without hitting your origin server; server-side object/page caching so your origin doesn’t rebuild the same page from the database on every request; choosing a data center geographically close to your actual visitors; and reducing database query time and plugin overhead on the origin server itself for requests that can’t be cached.
They’re planning-level estimates drawn from the general body of published web performance research linking page speed to conversion rate, which varies by industry and methodology from study to study. They’re meant as a reasonable starting assumption, not a precise guarantee for your specific site — you can and should overwrite the elasticity field with your own A/B test results if you have them, which will always be more accurate than an industry average.
Yes, and this simulator models that deliberately. The jump from a genuinely slow TTFB (1,200ms or more) to a merely mediocre one captures most of the available conversion benefit; squeezing the remaining milliseconds out of an already-fast site yields real but progressively smaller returns. A naive straight-line model would predict impossible results for very large improvements, which is why this tool caps the modeled lift instead.
Yes — network latency is bounded by the speed of light over real fiber routes, and a round trip between distant continents can easily add 100–250ms before your server has done any actual work. This is precisely the problem a CDN or edge cache solves: it puts a cached copy of your content physically close to the visitor, regardless of where your origin server actually lives.
Milliseconds aren’t a vanity metric. They’re a revenue lever.
TTFB is easy to dismiss as a technical detail buried in a PageSpeed report, but it’s the one number that delays literally everything else your visitor experiences — and every published study on the topic points the same direction: faster converts better. The question isn’t whether shaving milliseconds off your TTFB matters. It’s whether the dollar figure above is large enough to act on now.
Know what your milliseconds are actually worth before you decide whether to fix them.