What is a good reaction time?

Around 200–250 ms is quick for a visual cue, 250–300 ms is ordinary. Trained athletes in reaction sports sit near the bottom of that, and almost nobody beats about 150 ms honestly.

Why do my five rounds vary so much?

Because attention is not constant. Within-person variation of 50–100 ms across a handful of rounds is normal, which is why the average over five is more informative than any single round.

Reaction Time Test — How Fast Are Your Reflexes?

A typical human reaction to something you can see is around 250 ms. Much of that is nerve signalling, not thinking.

Most of your reaction time is not thinking

A typical click-on-green reaction lands near 250 ms, and very little of that is decision. Light has to reach the retina, the signal has to cross several synapses to the visual cortex and on to motor areas, and the muscle itself takes time to contract. The deciding part is a small slice of a mostly fixed budget.

How it works

Runs five rounds, each with a randomised wait so the green cannot be anticipated.
Measures with performance.now(), which is monotonic and sub-millisecond, rather than Date.now().
Reports your average and best round, and places you against a typical visual reaction time.

reaction = time of click − time the pad turned green

rough budget for a visual reaction:
  retina and optic nerve      ~ 50 ms
  visual processing           ~ 60 ms
  decision and motor planning ~ 80 ms
  nerve to muscle, contraction ~ 60 ms

Worked example

Five rounds from one person.

281 ms
243 ms
312 ms
236 ms
268 ms
average = 1340 / 5 = 268 ms

268 ms is squarely typical. The 312 ms round is not a failure — attention wanders, and the spread within one person is often 60–80 ms.

Reading the result

Your input hardware is part of the measurement. A high-refresh screen and a wired mouse can show 20–30 ms faster than a 60 Hz display with a Bluetooth trackpad, on identical reflexes.
Reaction to sound is faster than to light, typically by 30–40 ms, because the auditory path to the brainstem is shorter. Sprint starts use a gun for exactly this reason.
Clicking before green is not scored. Guessing the moment measures anticipation, which is a different thing and would flatter the result.
Reaction time is a rough, noisy measure of alertness. It is not a diagnostic of anything, and a slow day is usually sleep, caffeine or attention rather than neurology.

Common questions

What is a good reaction time?: Around 200–250 ms is quick for a visual cue, 250–300 ms is ordinary. Trained athletes in reaction sports sit near the bottom of that, and almost nobody beats about 150 ms honestly.
Why do my five rounds vary so much?: Because attention is not constant. Within-person variation of 50–100 ms across a handful of rounds is normal, which is why the average over five is more informative than any single round.