The number on your screen is not the number in your nervous system
When a reaction test reports 280 milliseconds, that figure covers everything between the panel changing colour and the code recording your click. Only part of it is you. The rest is a chain of machinery, each link adding a few milliseconds that nobody can see and that you cannot remove by trying harder.
This matters because the published research everyone quotes was not gathered this way. The most cited modern figure — a mean simple reaction time of 231 ms in Woods and colleagues (2015), from 1,469 adults — came from purpose-built laboratory apparatus. A site that shows you raw browser milliseconds next to that 231 ms is comparing two different measurements and letting you conclude you are slow.
Where the extra milliseconds come from
Four links in the chain, roughly in order of size:
- Display refresh. A 60 Hz screen only draws a new image every 16.7 ms. When the code decides to turn the panel green, the panel is not green yet — it becomes green at the next refresh, on average about 8 ms later, and up to 16.7 ms. A 120 Hz or 144 Hz display halves or better this, which is a real, measurable advantage that has nothing to do with the player.
- Pixel response. The panel then has to physically change. On a good OLED this is close to instant; on an ordinary LCD it takes a handful of milliseconds for the change to be visible enough to trigger you.
- Input sampling. A mouse reports its state at a fixed polling rate — 125 Hz on many office mice, which means up to 8 ms sitting between your physical click and the computer knowing about it. Gaming mice at 1000 Hz reduce this to about 1 ms. Bluetooth adds more than a wired connection.
- The software stack. The operating system delivers the event, the browser queues it, and JavaScript timestamps it. Each hop is small, but the browser's own event loop can be busy with rendering or garbage collection at exactly the wrong moment.
Added up, published measurements of online experiment platforms put the total overhead at roughly 71 to 87 milliseconds (Anwyl-Irvine and colleagues, 2021). That is why this site subtracts a documented 80 ms before comparing your time with laboratory norms, and describes the result as an estimate rather than a measurement. Your own machine may add more or less.
What we measured while building this
Two findings from building the tests, neither of which appears in the literature because they are engineering facts rather than psychology.
A background tab wrecks timing outright. Browsers deliberately slow timers in tabs you are not looking at, to save battery. We ran all six tests through an automated harness while the tab sat in the background: rounds that normally complete in about two seconds blew past a twenty-five second budget. This is not a small bias you could correct for, it is a broken measurement. It is also invisible — the test still produces a number. That is why every timed test here refuses to run while the tab is hidden and shows a notice instead. If a reaction site happily records a score while you are in another tab, treat its numbers with suspicion.
Colour transitions leak into the measurement. An early version of our reaction stage had a 120 ms CSS transition on the colour change, because it looked smoother. It also meant the stimulus arrived gradually rather than at an instant, so part of that fade sat inside every recorded time. We removed the transition entirely. Any test where the go-signal eases in rather than snapping on is measuring the animation as much as the person.
How much does this actually move your score?
Enough to change the story you tell yourself, and not enough to change who you are. Consider two people with identical nervous systems. One is on a 144 Hz monitor with a 1000 Hz wired mouse; the other is on a 60 Hz laptop screen with a Bluetooth mouse. The hardware difference alone can account for something in the region of 20 to 30 milliseconds, which is comparable to the gap between an average result and a good one.
Against that, Woods and colleagues found within-person variability of roughly 40 ms — meaning your own trials swing that much around your own average, run to run. This is the reason a single round is nearly meaningless and why this site scores the median of five. It is also why chasing a personal best on one lucky click tells you less than watching your median across a week.
How to read your own number
Treat the absolute figure as approximate and the comparison with yourself as real. Hold the conditions still: same device, same input method, same browser, tab in the foreground, similar time of day. Under those conditions a 15 ms improvement across several sessions probably means something. Across different devices, a 30 ms difference might mean nothing at all.
And be suspicious of round numbers that sound impressive. Human simple visual reaction time does not go below roughly 100 ms — that is the floor imposed by nerve conduction and muscle activation, not by effort. Anything faster than about 150 ms on a browser test is almost certainly anticipation rather than reaction, which is exactly why the delay before the go-signal here is randomised and early clicks are voided.
Frequently asked questions
Does my monitor's refresh rate really matter?
Yes, and it is one of the larger hardware factors. At 60 Hz the image can only change every 16.7 ms, so on average you lose about 8 ms waiting for the next frame. At 144 Hz that average drops to under 4 ms. It is a genuine advantage, which is worth remembering before comparing your laptop score with someone's gaming setup.
Is a wired mouse faster than Bluetooth?
Usually, by a few milliseconds. Polling rate matters more than the connection itself: a 125 Hz mouse can sit on your click for up to 8 ms, while a 1000 Hz one holds it for about 1 ms. Touchscreens behave differently again, generally slower and more variable.
Why does the test void my click if I go too early?
Because a click that lands before the signal is not a reaction to anything. If early clicks counted, the winning strategy would be rhythmic guessing, and the test would measure patience rather than speed. The wait is randomised so that guessing cannot be timed, and any round clicked during the red phase is discarded rather than scored.
Can I compare my score here with another site?
Only loosely, and only if you know what each site does. Sites differ in whether they subtract a hardware offset, whether they score the median or the mean, how many rounds they run, and whether they discard early clicks. A 250 ms on a site that reports raw means is not the same measurement as 250 ms here. Comparing your own history within one site is the comparison that survives.
Would a native app be more accurate?
Somewhat. A native application removes the browser layer but not the display, the input device or the operating system, so it narrows the gap rather than closing it. Genuine laboratory precision needs dedicated hardware — a response box rather than a mouse, and a screen whose refresh timing is known to the millisecond.