Reaction Time Test
How fast are your reflexes? Click the box the instant it turns green — 5 rounds, timed to the millisecond.
Runs 100% in your browser•No sign-up•Free forever
Ready to test your reflexes?
Click Start, then click the box the instant it turns green.
Your results
| Round | Time |
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This is a fun, approximate browser-based test — not a scientific or medical instrument. Your measured time includes your device's screen refresh rate, input latency, and browser/OS rendering delay, which can add roughly 20–80ms of noise on top of your true reaction time. The percentile comparison above is a rough, illustrative estimate for fun — not a scientific ranking. Use it to track your own trend over time, not as an exact clinical measurement.
Your history
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About this reaction time test
ReflexZap is a free browser-based reaction time test. It measures the time between the moment a visual cue appears (the box turning green) and the moment you respond by clicking or tapping. This is called simple visual reaction time — one of the most common ways to measure how quickly your nervous system processes a stimulus and triggers a motor response.
Everything runs client-side using your browser's high-precision timer — nothing is uploaded to a server, and your results are stored only on your own device via your browser's local storage.
Frequently asked questions
What's a good reaction time?
For simple visual reaction time, most healthy adults land somewhere between about 200 and 300 milliseconds. Under 200ms is unusually fast for a browser-based test (and may include some clicks that were a little anticipatory rather than purely reactive). Times creeping past 350ms are still completely normal — reaction time varies a lot based on tiredness, age, screen refresh rate, and how much coffee you've had.
How is reaction time measured on this site?
Each round, the box waits a random delay between 2 and 5 seconds before turning green, so you can't predict exactly when it will happen. The moment it turns green is recorded using the browser's high-resolution timer, and the moment you click or tap is recorded the same way. The difference between those two timestamps is your reaction time for that round. We run 5 rounds per session and show your average and your fastest single round.
What happens if I click too soon?
If you click before the box turns green, you'll see a brief "Not yet!" flash — that means you jumped the gun. The round doesn't count against you; it simply restarts with a fresh random delay. This keeps the test measuring genuine reaction to the stimulus rather than a guessed or timed click.
Is this test scientifically accurate?
It's a fun, approximate measurement, not a clinical or laboratory instrument. Browser JavaScript timers, screen refresh rates (typically 60Hz, meaning a new frame only appears roughly every 16.7ms), input device polling rates, and general system load all add a bit of extra latency on top of your true biological reaction time. Lab equipment used in vision-science research eliminates most of this noise with dedicated hardware. Treat your results here as a relative, repeatable way to track your own reflexes over time rather than an exact number.
Can reaction time be improved?
Somewhat. Reaction time tends to be faster when you're well-rested, alert, and free of distractions, and tends to slow with fatigue, alcohol, certain medications, and age. Practice can modestly improve your performance on a specific test like this one as you get used to the rhythm, but the underlying biological reaction speed changes only gradually, if at all.