How the test works
Press Click to start. The box turns red and shows Wait for green…. After a random pause of 2 to 5 seconds it switches to green with Click now!, and the clock starts. Click the box, tap it, or press Space or Enter. The time from the green colour to your press appears in milliseconds, and the next attempt starts when you click again.
There are five attempts. If you press while the box is still red, you see Too soon!: that attempt is thrown away and you simply try it again, so guessing the moment never improves your score. Because the pause is random, you cannot learn the rhythm either. If you want to see how fast you can repeat a movement rather than how fast you respond, try the finger tapping test.
After the fifth attempt the result card shows your Average of the five, your Fastest attempt and a plain-language rating. The card also saves your score in this browser, so the next time you play you see your personal best and a small chart of your last results. Reset clears the current round without touching your saved best.
What happens in those milliseconds
A simple reaction looks instant, but it is a chain. Light from the green box hits your retina, which turns it into nerve signals. Those signals travel to the visual areas at the back of your brain, which recognise "it changed". Your brain then sends a command down to the muscles of your finger, and the finger has to move far enough to press the button. Each step takes time, and the total is what you see on screen.
The Dutch physiologist Franciscus Donders was one of the first to time this chain, in the 1860s. He showed that a reaction with only one possible stimulus and one possible response (what this test measures) is the fastest kind. As soon as you have to choose between responses, the time grows, which is what our choice reaction time test explores.
How to read your score
A long-standing figure from laboratory research is that young adults need about 190 ms on average to react to a light. Robert Kosinski's A Literature Review on Reaction Time (Clemson University) summarises it, citing A. T. Welford's book Reaction Times (Academic Press, 1980). Laboratory equipment uses a lamp and a dedicated button with almost no delay.
A browser test cannot do that. Your screen needs time to draw the green frame, and your mouse, keyboard or touchscreen needs time to report the press. Together this usually adds 20 to 60 ms. That is why the result card compares you with about 250 ms: roughly the laboratory figure plus the delay of an ordinary computer or phone. The rating on the card uses these steps:
- under 180 ms: Excellent
- 180 to 249 ms: Faster than average
- 250 to 319 ms: About average
- 320 ms or more: Slower than average
Look at the average more than the fastest attempt. One very quick press can be partly luck; five steady presses say more about you.
What changes your reaction time
Some influences come from you, not the device:
- Sleep and tiredness. Reaction time is one of the first things to suffer after a short night. If your average is suddenly slower than your saved best, tiredness is a likely reason.
- Age. Simple reaction time gets slower across adulthood. The change is gradual, and practised people keep fast reactions for a long time.
- Attention. A wandering mind costs more than slow muscles. Look at the box, not at the result list, while you wait.
- Warm-up. The first attempt is often the slowest. Play a full round, then play again and compare.
- Alcohol and some medicines slow reactions. Never use an online result to decide whether you are fit to drive.
How to get faster
Real gains come from steady habits rather than tricks. Rest well, sit so that your finger already touches the button, and keep your eyes on the centre of the box. Short daily sessions work better than one long one, because your attention fades after a few minutes. On the device side, a wired mouse or the keyboard is usually quicker than a touchscreen, and a higher refresh rate shows the green slightly earlier.
To see how much of your speed is down to your eyes, try the audio reaction time test on the same device: you react to a beep instead of a colour, and the result card compares the two. If you want to add precision to speed, the aim test times how quickly you reach and hit targets that appear at random places.
Limits of an online test
Your score always includes your hardware, so compare yourself on the same computer or phone, not with a friend on a different one. A slow or busy device, a television without game mode or a Bluetooth mouse can all add delay that has nothing to do with you. This is a self-check for curiosity and practice, not a medical test. If you notice that your reactions have become much slower in everyday life, for example while driving, talk to a doctor rather than relying on a website.
More tests of speed and timing are collected on the reflex and speed tests page.
Sources
- Donders, F. C. (1969). On the speed of mental processes (W. G. Koster, Trans.). Acta Psychologica, 30, 412–431. (Original work published 1868)
- Welford, A. T. (Ed.). (1980). Reaction times. Academic Press.
- Kosinski, R. J. (n.d.). A literature review on reaction time. Clemson University.
Frequently asked questions
What is a good reaction time on this test?
The result card compares you with about 250 ms, which is roughly the laboratory average for a visual reaction (about 190 ms) plus the 20 to 60 ms that a normal screen and mouse add. Under 180 ms is rated Excellent, 180 to 249 ms Faster than average, 250 to 319 ms About average and 320 ms or more Slower than average.
Why do I have to do five attempts?
A single press can be lucky or unlucky. The average of five attempts is much more stable, so it is a better picture of your real speed and a fairer number to compare with your personal best.
What happens if I click too early?
If you press while the box is still red you see Too soon! and that attempt does not count. You repeat it after a new random wait of 2 to 5 seconds, so guessing never helps.
Where is my personal best saved?
Only in this browser, on this device. Nothing is uploaded. Clearing your browser's site data or using a private window removes it.
Why is my score slower on my phone than on my computer?
Touchscreens and many phone displays add more delay than a wired mouse and a fast monitor. Your nerves are the same, but the device adds milliseconds, so compare results on the same device.
Can I train my reaction time?
You can usually improve a little with rest, focus and practice, mostly by becoming more consistent. Large jumps tend to come from better hardware or simply from being less tired.
Is a slow result a sign of a health problem?
No single online result can tell you that. Tiredness, distraction and the device all change the number. If your reactions feel clearly slower in daily life, talk to a doctor.
Is this the same as a reflex exam at the doctor?
No. When a doctor taps your knee with a small hammer, the leg moves on its own, without any decision from you. This page measures your simple visual reaction time: how long it takes you to notice a colour change and press a button.