Does being tired slow your reaction time?
The short answer
Yes — significantly. Fatigue is one of the most powerful modulators of reaction time, and the effects compound quickly. After 17–19 hours awake, impairment reaches the equivalent of a 0.05% blood alcohol concentration. After 24 hours, it equals ~0.10% BAC.
The data
| Hours awake | RT impact | BAC equivalent |
|---|---|---|
| 14h | ~+10ms | ~0.02% |
| 17h | ~+30ms | ~0.05% |
| 20h | ~+50ms | ~0.08% |
| 24h | ~+70ms | ~0.10% |
| 28h | ~+100ms+ | Above legal limit in all jurisdictions |
What it means for you
The insidious feature of fatigue-related RT slowing is that subjective feelings of tiredness become less accurate as sleep deprivation increases — you may feel "fine" while being significantly impaired. This is why sleep scientists consider drowsy driving as dangerous as drunk driving.
If your Reaction Time test score is significantly worse than usual, poor sleep is the most likely explanation. Take the test after a good night's rest and compare.
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Quick Answer
Significantly. After 17–19 hours awake, RT impairment equals 0.05% blood alcohol. After 24 hours without sleep, impairment approaches 0.10% BAC - above legal driving limits in most countries.
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