What is reaction time?

Definition

Reaction time is the interval between a stimulus appearing and your body starting to respond. It is a start time, not a completion time: the clock stops when your finger begins to move, not when the click lands. That is why a fast reaction and a fast click are different measurements.

Visual versus auditory

Visual reactions average roughly 250–280 ms. Auditory reactions run 30–50 ms faster, because sound reaches the brain quicker than light has to be processed by the visual cortex. It is the reason sprinters start on a bang rather than a flash.

What moves your score

Sleep, caffeine, arousal level, warm-up, display refresh rate, input device, and whether your attention was actually on the screen. Each of those is worth tens of milliseconds — more than the difference between “average” and “good” on any benchmark table you will find online.

Can you actually train it?

You can reliably recover milliseconds you are losing to fatigue, cold hands and distraction, and practice gives a modest genuine improvement. You cannot turn a 300 ms human into a 120 ms one. Anyone promising that is selling a subscription — and the cognitive-training industry has already been fined once for exactly that kind of claim.

Why most websites measure it badly

Three common faults: using a wall-clock function that can jump when the system clock adjusts; leaving advertising that reflows the page mid-test, which shifts the moment you actually see the signal; and accepting any click as valid, so a held mouse button or a macro produces a heroic score. Fixing all three costs nothing, which is why we did.