Alcohol & Sleep Calculator
Alcohol is the most commonly used sleep aid in the world, and one of the most counterproductive. This calculator shows your BAC at bedtime, how much REM sleep you'll lose, and what time you need to stop drinking to sleep without disruption.
The sedation trap
Alcohol creates an illusion of sleep quality. It reduces the time to fall asleep, which feels like better sleep. But sleep architecture under alcohol is profoundly abnormal: REM is suppressed in the first half, slow-wave sleep is elevated early, and then both invert in the second half as the rebound effect takes hold. The brain effectively completes a night of low-quality, fragmented sleep while you believe you slept soundly.
The subjective sense that "a drink helps me sleep" is accurate for one thing only: sleep latency. It is inaccurate for sleep quality, sleep continuity, and morning restoration, the things that matter most.
Related calculators
- Sleep Quality Score — 8-question assessment of your sleep health
- Caffeine Cutoff Calculator — another common sleep disruptor, timed correctly
- Sleep Deprivation Cost Calculator — the cognitive cost of disrupted sleep
Frequently asked questions
Does alcohol help you sleep?
Alcohol has a biphasic effect on sleep. In the first half of the night, its sedating properties can reduce sleep latency (help you fall asleep faster) and increase slow-wave sleep. But in the second half, as alcohol is metabolised, there is a rebound in arousal, sympathetic nervous system activity, and REM disruption. The net effect for most people is earlier sleep onset but more fragmented, less restorative sleep overall, particularly in the second half of the night when REM would normally dominate.
How much does alcohol reduce REM sleep?
Ebrahim et al. (2013) meta-analysis found that low, moderate, and high doses of alcohol reduced REM sleep by 9.3%, 24.2%, and 39.2% respectively in the first half of the night. Each 0.01% BAC at bedtime suppresses approximately 9 minutes of REM sleep. A BAC of 0.05% at bedtime, achievable with 2–3 drinks for many people, eliminates most of the first-cycle REM sleep. Since early morning sleep is REM-dominant, alcohol consumed in the evening robbing the second half of the night may eliminate more REM than first-half estimates suggest.
How long before bed should I stop drinking?
For minimal sleep disruption, alcohol should be cleared to below 0.02% BAC before you sleep. At a standard elimination rate of 0.015% BAC per hour, a BAC of 0.08% (the typical legal driving limit) takes about 4 hours to drop below 0.02%. Practical guidance: stop drinking at least 3–4 hours before bed for low drink counts (1–3 drinks), and 6+ hours for heavier consumption. Body weight, sex, and whether you've eaten all significantly affect the timeline, use the calculator for a personalised estimate.
Why do I wake up at 3am after drinking?
The '3am wakeup after drinking' is one of the most consistent subjective reports about alcohol and sleep, and it has a clear physiological explanation. Alcohol suppresses the stress hormone norepinephrine in the first hours of sleep, increasing deep sleep. As alcohol is metabolised 4–5 hours later, norepinephrine rebounds sharply above baseline, causing arousal, increased heart rate, sweating, and the characteristic early morning waking. The timing corresponds to when most of the alcohol has been cleared from the system.
For informational use only. Never drink and drive. If alcohol use is affecting your health, please speak to a healthcare professional.