Reaction time test
Click, tap, or press Space the instant the stage turns green. It starts neutral, goes red for a random wait, then turns green and starts the clock. Run five attempts to get a best and a mean, measured to the millisecond.
How it works
Reacting to a signal is not one event, it is a short pipeline with three stages, and every one of them takes real time:
- Perception. Light from the newly green screen reaches your eyes, and the signal travels from the retina through the visual system until the brain registers "that changed."
- Decision. The brain confirms the change matches the rule ("green means go") and selects the response — trivial for a single fixed signal like this one, which is why simple reaction time is faster than choice reaction time, where the brain must also pick which of several possible responses is correct.
- Motor execution. A nerve signal travels back out to the relevant muscles, they contract, and the muscle movement itself takes a small but non-zero amount of time to register as a click, tap, or key press.
None of that is optional or skippable, which is exactly why nobody's reaction time is 0ms and why even the fastest recorded simple reaction times in controlled lab studies still sit above roughly 100ms.
What this number actually measures
Be honest about what a browser can and cannot isolate: the number this test reports is the whole chain, not just your nervous system. Two extra delays are baked in on top of biology, and there is no way for any browser-based test to strip them back out:
- Display latency. A screen does not become green the instant the page tells it to. It waits for its next refresh cycle, and depending on the panel, that can add anywhere from a few milliseconds on a fast, high-refresh-rate display to considerably more on a slow one.
- Input latency. A mouse or keyboard reports its state on its own polling schedule, a touchscreen has its own touch-to-registration delay, and Bluetooth peripherals in particular can add noticeably more lag than a wired connection.
Because of this, absolute numbers from this test — or any browser-based reaction time test — are device-dependent. Comparing your own result against your own result on the same device and browser is meaningful and fair. Comparing your number against someone else's on a different phone, mouse, or monitor is comparing two different measurement chains, not two brains.
Timing method used by this page
The moment the stage turns green, the page captures a timestamp from performance.now(). The click, tap, or key press that ends the wait carries its own high-resolution timestamp, event.timeStamp, and the two are on the same clock — both are DOMHighResTimeStamp values sharing one time origin, so subtracting one from the other is valid arithmetic with no unit conversion and no risk of mixing in Date.now(), which runs on a different, coarser clock. Nothing about the time the browser spends rendering the change is added to the result beyond what genuinely happens before your input reaches the page.
Getting a fair reading
- Use the same device for comparisons. Your own trend over time, on the same phone or computer, is far more meaningful than a single absolute number.
- Rest your hand or finger near the target before the run starts, the same way a sprinter sets their blocks — reaching for the screen adds motor time that has nothing to do with reaction speed.
- Stay alert. Fatigue, distraction, and divided attention all measurably slow reaction time; running the test mid-multitask will not reflect your best number.
- Ignore any single outlier. One slow attempt in a run of five is normal variability, not a real change in ability — that is exactly why the mean matters alongside the best.
- Expect early attempts to be slower. Familiarity with exactly when and how the stage changes shaves real milliseconds off, which is a learning effect on the task, not a change in underlying reflexes.
Use cases & limitations
Where this is genuinely useful
- Tracking your own trend. Run it the same way on the same device weekly and watch whether your number drifts, rather than treating any single run as definitive.
- A quick, honest curiosity check. How fast can you actually react to a colour change, with false starts caught rather than rewarded.
- Warm-up or awareness for reflex-dependent games and sports — a casual gauge before a session, not a training regimen on its own.
- Classroom or casual demonstrations of the perception-decision-motor pipeline described above.
What this tool cannot tell you
- Your true biological reaction time in isolation. Display and input latency are always mixed in — see the honest breakdown above.
- A clinical or diagnostic result. This is not a medical, neurological, or fitness-for-duty assessment, and unusually slow results here are not a diagnosis of anything.
- A fair comparison across different devices. The same person can score differently on a phone versus a gaming monitor purely from hardware differences.
- Choice reaction time. This tool only measures simple reaction time — one signal, one response. Tasks that require picking between multiple possible responses are reliably slower and are not what this test models.
Frequently asked questions
How is my reaction time actually measured?
The instant the stage turns green, the page records a high-resolution timestamp from performance.now(). When you click, tap, or press a key, the browser's own event carries its own high-resolution timestamp (event.timeStamp). Both numbers share the same clock, so subtracting one from the other gives the elapsed time directly, with no separate clock to get out of sync and nothing about screen rendering folded in by mistake.
Why do I get a different result every time I try?
Human reaction time is naturally variable from one attempt to the next — attention, fatigue, and simple neural noise all shift it by tens of milliseconds even in a single sitting. That is exactly why the test runs five attempts instead of one: a single number can be a lucky guess or a slow blink, but the best and the mean of five attempts are far more representative of your actual speed.
What counts as clicking too soon?
Any click, tap, or key press while the stage is still red counts as too soon. It is not scored, it is not counted as one of your five attempts, and the same attempt simply restarts. This stops you from beating the clock by guessing when green is about to appear rather than reacting to it.
Is 250 milliseconds a good reaction time?
For simple visual reaction time — react to one signal with one response, exactly what this test measures — healthy young adults commonly fall in roughly the 200-270 millisecond range under controlled laboratory conditions, so 250ms sits near the middle of that band. Online results tend to run somewhat higher because they include a screen's refresh delay and an input device's own lag on top of biological reaction time. See the average reaction time reference page for the sourced ranges.
Why is my score here slower than in a game I play?
Different games often measure different things. Some reward anticipation of a pattern rather than genuine simple reaction time, some average only your fastest attempts and discard the rest, and some run on hardware with a much higher refresh rate and a wired, high-polling-rate controller — both of which shave real milliseconds off the number before your brain is even involved. A slower number here is not necessarily a slower you; it may just be a stricter, more honest measurement.
Does my mouse, trackpad, or phone screen affect the result?
Yes, measurably. A budget touchscreen or a Bluetooth mouse can add tens of milliseconds of its own latency before your input even reaches the browser, and a low refresh-rate display delays how soon the green screen is actually visible to react to. This test cannot separate your biological reaction time from your device's — the number it reports is the whole chain, screen to muscle to click, which is also what any browser-based test measures whether or not it says so.
Can reaction time actually be improved with practice?
Somewhat. Practice mainly reduces false starts and familiarises you with the exact task, which trims the number over the first few sessions. Being well rested, alert, and free of the kind of divided attention that comes from multitasking also measurably helps. What practice does not do is rewrite basic nerve conduction speed — there is a floor set by biology that repetition alone will not push through.
Do you store or upload my results anywhere?
No server ever sees your reaction times. Everything runs in your browser, and the only thing saved is your single all-time best number, kept in this browser's localStorage purely so it can be shown back to you on a later visit. It never leaves your device, and clearing your browser's site data removes it.
Why does the delay change every time instead of staying fixed?
A fixed delay would let you count seconds and click on a schedule instead of actually reacting to the colour change, which would measure timing skill rather than reaction time. Randomising the wait between 1.5 and 4 seconds removes that shortcut, which is also why clicking during the red phase is specifically detected and discarded rather than scored as a very fast time.