Faced with a simple signal, an adult reacts in just over 200 milliseconds — about a fifth of a second. Yet driving instructors count one full second. Both numbers are right. Here is what each one measures, why an on-screen test always shows a bit more, and what makes your reflexes faster or slower.
The average reaction time: about a fifth of a second
Simple reaction time is the delay between an expected signal (a light, say) and your response (pressing a button). It is the "purest" reflex we can measure.
In 2015, researchers re-examined several large British studies carried out between 1888 and the 2000s. Once equipment delays were removed, the average simple reaction times fell between 208 and 238 milliseconds. So the number to remember for a healthy adult is about 0.2 seconds — with large differences from one person, and one attempt, to the next.
Why an online test shows more
On a computer or phone, the measured time also includes the screen's delay in displaying the signal, the keyboard, mouse or touchscreen delay, and the browser's own lag. In one of the re-examined studies, researchers had to subtract 53 milliseconds of screen lag, plus about ten more for the key press. A result of 260 or 280 ms on an online test is therefore perfectly normal — compare yourself with yourself, on the same device.
Simple vs choice reaction time
As soon as you have to choose (press left if the signal is red, right if it is green), reaction time gets longer: the brain must identify the signal, then select the right response. A large British survey published in 2006 by Geoff Der and Ian Deary followed more than 7,000 adults. Simple reaction time changed little until about age 50, whereas choice reaction time slowed throughout adulthood. Differences between men and women exist but are small, and say almost nothing about any one person.
Driving: why we count one second
On the road, things are far more complex than pressing a button in a lab. You must see the hazard, decide to brake, then move your foot from the accelerator to the brake pedal. Germany's ADAC motoring club puts that delay at 0.8 to 1.2 seconds, which is why driving instructors use one second in their calculations.
| Speed | Distance covered in 1 second of reaction |
|---|---|
| 30 mph (48 km/h) | about 13 metres (44 ft) |
| 50 mph (80 km/h) | about 22 metres (73 ft) |
| 70 mph (113 km/h) | about 31 metres (103 ft) |
During that second the car has not started braking yet; the braking distance comes on top. Tiredness, a phone or alcohol stretch the delay — every tenth of a second counts.
What slows your reflexes down (or speeds them up)
- Lack of sleep. A 2010 meta-analysis by Lim and Dinges found that sleep deprivation hits simple attention and reaction speed first, more clearly than reasoning. After a sleepless night you react more slowly and "zone out" more often.
- Age, especially for choice reactions, as described above.
- Practice on a specific task. You improve quickly on an exercise you repeat, partly because you learn to anticipate it.
- Anticipation. Moving before the signal is not a reflex, it is a gamble. In athletics, leaving the blocks less than 0.1 seconds after the gun counts as a false start.
Reflexes and attention: consistency matters as much as speed
Your best time says little; how consistent your times are says more about attention. A meta-analysis of 319 studies (Kofler and colleagues, 2013) showed that children and adults with ADHD have more variable reaction times, with occasional "attention gaps", without being slower on average once that variability is taken into account.
This variability also shows up with fatigue and in other conditions, so it is not a diagnostic sign on its own. If forgetfulness and frequent distraction get in your way every day, a structured questionnaire can help you take stock before talking to a doctor.
🧠Test yourselfADHD testAttention, organisation, impulsivity · 6 min · test in FrenchStart →How to test your reflexes
A good reaction time test repeats several trials, waits a random delay before each signal (so you cannot anticipate) and reports the median rather than your best try. Take it rested, somewhere quiet, and always on the same device if you want to compare results from one day to the next.
Test yourself
Frequently asked questions
What is the average human reaction time?
About 0.2 seconds (200 to 240 milliseconds) to a simple signal in the lab. On a screen the measurement is a little longer because of device delays.
What is the average reaction time for drivers?
About one second: you have to see, decide and move your foot. The ADAC puts it at 0.8 to 1.2 seconds; at 30 mph a car travels about 13 metres in that time.
Can you improve your reaction time?
You get faster at a task you practise, and good sleep clearly helps. Sleep deprivation, on the other hand, slows reactions markedly.
Is a slow reaction time a cause for concern?
A single measurement means very little: fatigue, the device and distraction all change it. If you notice a clear change in daily life, talk to a doctor.
Sources
- Woodley of Menie M. A., te Nijenhuis J., Murphy R. (2015). The Victorians were still faster than us. Commentary: Factors influencing the latency of simple reaction time. Frontiers in Human Neuroscience, 9, 452. — doi.org/10.3389/fnhum.2015.00452
- Der G., Deary I. J. (2006). Age and sex differences in reaction time in adulthood: Results from the United Kingdom Health and Lifestyle Survey. Psychology and Aging, 21(1), 62–73. — doi.org/10.1037/0882-7974.21.1.62
- Lim J., Dinges D. F. (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychological Bulletin, 136(3), 375–389. — doi.org/10.1037/a0018883
- Kofler M. J. et al. (2013). Reaction time variability in ADHD: A meta-analytic review of 319 studies. Clinical Psychology Review, 33(6), 795–811. — doi.org/10.1016/j.cpr.2013.06.001
- ADAC — Reaktionsweg berechnen : la règle « vitesse ÷ 10 × 3 » et 0,8 à 1,2 seconde de réaction. — adac.de/verkehr/rund-um-den-fuehrerschein/erwerb/reaktionsweg-berechne
- ADAC — Bremsweg berechnen : la règle « (vitesse ÷ 10) × (vitesse ÷ 10) » pour un freinage normal. — adac.de/verkehr/rund-um-den-fuehrerschein/erwerb/bremsweg-berechnen/
The MyMindTests team writes about the brain from published studies. Every figure is sourced and checked before publication.