What factors affect reaction time?
The short answer
Reaction time is influenced by a wide range of biological, psychological, and environmental factors. Here are the most significant ones, with approximate effect sizes:
The biggest fixed factor is age: reaction time peaks in the mid-20s and then slows gradually, by roughly 3-5ms per decade. Around that baseline, day-to-day state matters more than most people expect. Sleep is the largest controllable variable - one night of deprivation adds about 50ms, and staying awake 17-19 hours impairs you to roughly the level of a 0.05% blood alcohol concentration. Caffeine works in the opposite direction, with 100-200mg cutting around 10ms, while alcohol at 0.08% BAC adds roughly 30ms.
The data
| Factor | Effect on RT | Direction |
|---|---|---|
| Age (peak ~20–25) | 3–5ms per decade | Slows with age |
| Sleep deprivation (1 night) | ~50ms | Slower |
| Caffeine (100–200mg) | ~10–15ms | Faster |
| Alcohol (0.08% BAC) | ~30ms | Slower |
| Auditory vs visual stimulus | ~30–50ms | Faster for sound |
| Device / hardware latency | ~20–50ms | Added to every score |
| Warm-up / practice | ~15–20ms | Faster |
| Temperature (cold hands) | ~5–15ms | Slower |
| Stress / anxiety | ~10–20ms (varies) | Faster at low; slower at high |
| Fatigue (end of long task) | ~20–40ms | Slower |
| Action video game training | ~15–20ms | Faster |
| Stimulus expectancy | ~20–40ms | Faster when expected |
What it means for you
Two factor groups are easy to overlook. The first is stimulus modality: auditory reaction times are about 30-50ms faster than visual ones, because sound reaches the brain through a shorter processing pathway. The second is your equipment - display lag and input latency on a typical setup add 20-50ms to any online score, which is why results are only truly comparable when taken on the same device. Arousal follows the Yerkes-Dodson curve: moderate alertness produces the fastest responses, while both drowsiness and high anxiety slow you down. Temperature and time of day matter at the margins - cold hands respond more slowly, and most people are quickest from late morning to early evening, when core body temperature is highest.
Treat the table above as a pre-test checklist. If you want your best possible score, test rested, moderately caffeinated, warmed up, alcohol-free, and on a low-latency device. If you want to track genuine change over time, hold those variables constant instead. Sleep is the variable most worth understanding in depth, since it has the single largest day-to-day effect - see how sleep quality affects reaction time for the full breakdown.
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Quick Answer
Age, sleep quality, caffeine, alcohol, stress, temperature, practice, and stimulus type all affect RT. Sleep deprivation alone adds ~50ms. Alcohol at 0.08% BAC adds ~30ms.
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