What this test measures
The panel starts red with the words "Wait for green." After a random delay of 1.5 to 4 seconds it turns green, and your job is to click or tap the instant you see the change. The time between the color change and your click is your simple reaction time: how long it takes you to detect a single expected signal and respond to it.
You get five rounds. Your score is the median of the five, and your single best round is shown alongside it. If you click while the panel is still red, that round is voided as "too soon" and does not count toward anything. The delay is randomized precisely so you cannot time it; guessing is the thing being filtered out.
One quirk: if the browser tab is hidden, the test refuses to run. Browsers throttle timers in background tabs to save battery, which would corrupt the measurement, so the test simply waits until the tab is visible again.
The science
The comparison figures on this page come from published research, not from a database of other visitors' scores. The anchor study is Woods and colleagues (2015), who measured simple reaction time in 1,469 adults aged 18 to 65. Their participants averaged 231 ms, or about 213 ms once the researchers corrected for the 17.8 ms of delay introduced by their own testing hardware. Individuals differed from one another with a between-subject standard deviation of 26.8 ms, and reaction time crept upward with age at about 0.55 ms per year.
Your browser adds its own delay, and it is not small. Anwyl-Irvine and colleagues (2021) measured response delays across web browsers, operating systems, and devices on four online experiment platforms and found averages between 71.33 and 87.40 ms. That lag sits between your finger and the timestamp the page records, and it counts against you.
Because of this, the site subtracts a flat 80 ms device offset from your score before comparing it with the Woods data. Your actual hardware may add more or less than 80 ms, so treat the percentile as an estimate rather than a measurement. Two people with identical nervous systems can post different numbers here purely because one of them is on a faster machine.
What counts as a good reaction time
For a simple visual task like this one, a typical adult reacts in roughly 200 to 250 ms of true neural and muscular time. In the Woods sample, most people fell between about 186 and 240 ms, which is the corrected mean of 213 ms plus or minus one standard deviation. A true reaction time under about 185 ms already makes you faster than most adults in that sample.
On this test, though, think in on-screen numbers. With typical browser latency added back, an average adult should expect a displayed median somewhere around 280 to 300 ms. A displayed 250 ms is quick. A displayed 220 ms or lower is rare, and at that level you should suspect your hardware is flattering you a little.
Age shifts the picture slowly. At 0.55 ms per year, the average 60-year-old is only about 22 ms slower than the average 20-year-old. That gap is smaller than the round-to-round noise in your own results, so a sluggish score on any given day says more about the day than about you.
Why your score jumps around
Run the test twice and you will probably get two different numbers. That is expected. Woods and colleagues found intra-subject variability of roughly 40 ms, meaning one person's individual trials routinely swing that much around their own average. Five rounds will not smooth this out completely, but it is enough to make the median meaningful.
The median is used instead of the average because it shrugs off outliers. One distracted round of 500 ms would drag an average badly but barely moves a median. A lucky anticipation that slips through past the red-click filter does the same in the other direction. The best-round figure is shown because it is satisfying to see, but the median is the honest number.
Hardware adds noise of its own. Screen refresh timing, input polling, and operating system scheduling all vary from moment to moment, and that jitter is part of the 71 to 87 ms of platform delay in the Anwyl-Irvine data. Background tabs are worse than noisy: browsers deliberately slow their timers, which is why the test refuses to run when the tab is hidden instead of serving you a corrupted result.
How to improve it
Honestly, not by much. Simple reaction time is a fairly stable trait, and most of the improvement people see comes from measurement conditions rather than from a faster brain. The conditions are still worth controlling:
- Sleep. Reaction-time tasks are a standard laboratory probe for sleep deprivation. If you test while exhausted, you are measuring the exhaustion.
- Caffeine timing. If you are a regular coffee drinker, test after your usual cup rather than before it. Consistency matters more than the dose.
- Practice. Expect your first session to be your worst. Early gains mostly reflect learning the task itself, such as where the panel sits and how the click feels, and they flatten quickly.
- Posture and hand position. Rest your finger on the mouse button or hover your thumb just over the screen. Travel distance is dead time.
- Screen refresh rate. A 60 Hz display draws a new frame every 16.7 ms, so the green can appear late. A 144 Hz monitor cuts that wait. This improves your displayed score without changing you at all.
If you are chasing a number, run full five-round sets and compare medians across days rather than celebrating single flukes.
Frequently asked questions
Am I being compared against other users of this site?
No. The percentile comes from published research, chiefly the 1,469-adult Woods dataset, with an 80 ms offset subtracted from your score to account for typical browser and device delay. There is no hidden leaderboard database behind it.
Why was my round voided as "too soon"?
You clicked while the panel was still red. That means you were predicting the change rather than reacting to it, and a prediction says nothing about your reaction time. The randomized 1.5 to 4 second delay exists to make prediction unprofitable; a voided round is that filter doing its job.
Why is my phone slower than my computer?
Different devices carry different amounts of input and display latency, and touchscreens process a tap through their own sensing pipeline before the page ever hears about it. The Anwyl-Irvine study found delays varying across the browsers, operating systems, and devices they measured. The 80 ms correction is a single average, and your particular phone may sit above it.
Is 300 ms a bad score?
Displayed on this test, no. Subtract the 80 ms estimate for device delay and you are at roughly 220 ms of true reaction time, close to the corrected average of 213 ms from the Woods study. It is an ordinary, healthy number.
Why will the test not start in a background tab?
Browsers throttle JavaScript timers in tabs you are not looking at, sometimes severely. Any measurement taken under throttling would be garbage, so the test declines to run at all until the tab is visible.