Time to First Byte Calculator

Break time to first byte into network and server components.

About Time to First Byte Calculator

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.

Formula

Time to First Byte

TTFB = DNS + TCP + TLS + server processing + response transfer

good threshold: 800 ms
connection overhead: DNS, TCP and TLS combined

Worked example

With the default values below, Time to First Byte Calculator returns Time to First Byte of 430. Change any input above and every figure here is recalculated in your browser.

Inputs used

DNS lookupminimum 0 ms: 40 ms
TCP connectionminimum 0 ms: 60 ms
TLS negotiationminimum 0 ms: 80 ms
Server processingminimum 0 ms: 220 ms
Response transferminimum 0 ms: 30 ms

Results

Time to First Byte: 430 ms
Rating: Good
Connection Setup Overhead: 180 ms
Largest Component: Server processing — optimise the backend or add caching
Estimated Saving From a CDN: 108 ms

Step by step

1Values used
2Time to First Byte
3Time to First Byte= 430 ms
4Rating= Good
5Connection Setup Overhead= 180 ms
6Largest Component= Server processing — optimise the backend or add caching
7Estimated Saving From a CDN= 108 ms

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Time to First Byte calculated?

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.

Why does Time to First Byte matter?

Because every downstream metric inherits TTFB, it is usually the highest-leverage single optimisation on a slow site.

What values do I need to enter?

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.