Reaction Time Test

For a simple visual stimulus, a colour change on screen followed by a click, the average adult reaction time is about 250 milliseconds. Roughly 200 ms is fast, 300 ms is a little slow, and anything under 150 ms on this test almost always means you anticipated the change rather than reacted to it. Elite athletes and competitive gamers cluster around 150–200 ms; sprint rules treat a start faster than 100 ms after the gun as a false start because that is below the limit of human response.

The number breaks down into stages: the eye registers the change (30–50 ms), the signal reaches the brain and a decision is made (100–150 ms), and the motor command travels to the finger and the muscle contracts (50–80 ms). The input device adds a little on top: a wired mouse or a keyboard responds in a few milliseconds, a touchscreen in 20–50 ms, and a wireless mouse on a busy network can add more. Compare results on the same device, not across devices.

Take at least five attempts and use the average; a single trial is mostly noise. Sit close to the screen, keep your finger resting on the button, and look at the centre of the box rather than the edges. "Too soon" means you clicked before the colour changed, which is anticipation, not reaction; the test discards that attempt. The colour change is delayed by a random interval so that you cannot learn a rhythm.

Consistency matters more than any one fast score. Athletes track the spread of their times as well as the mean, because a wide spread indicates lapses of attention. The best-of and average shown under the results let you watch both.

• Sleep. One short night slows reaction time by a measurable margin; a week of six-hour nights produces impairment comparable to being over the drink-drive limit in several studies. If your score is unusually slow, this is the first thing to check.
• Caffeine. A moderate dose improves reaction time by around 5–10 % for a few hours. Large doses add jitter and false starts.
• Age. Reaction time is fastest in the mid-twenties and lengthens by a few milliseconds per year afterwards. Regular exercise slows the decline.
• Practice. Simple reaction time improves only slightly with training; what improves a lot is the choice reaction time used in sport and gaming, where you must pick the right response, not just any response.
• Alcohol, fatigue, distraction and illness all slow it, which is why the test is used in research on driving and workplace safety.

Measure how consistent you are over a longer effort with the stopwatch and lap timer, or test a different skill with the typing speed test. If sleep is the likely cause of a slow score, our guide to sleeping and waking well is the place to start.