Sleep & wake-up
Alcohol and sleep calculator
Estimate how long alcohol takes to clear your system and whether it will still be processing at bedtime.
A standard drink is about 14 g of pure alcohol: a 350 ml beer, a 150 ml glass of wine or a 44 ml shot of spirits. This is general guidance, not a blood-alcohol or legal-driving estimate.
How the clearing time is estimated
The tool uses the Widmark approach, the standard way to approximate alcohol in the body. Each standard drink is treated as 14 grams of pure alcohol. Peak blood alcohol is the alcohol in grams divided by your body weight times a distribution factor (about 0.66 across adults), and the body then removes alcohol at a steady rate of roughly 0.015 percentage points per hour. Dividing the peak by that rate gives the hours to clear. For 3 standard drinks at 70 kg, that is about 42 g of alcohol, a peak near 0.09%, and roughly 6 hours to return to zero. The calculator adds that span to your last drink to estimate when you will be clear, and compares it with your bedtime.
These are population averages. Your real rate depends on sex, liver health, food in your stomach, medication and genetics, so treat the time as a ballpark. It is not a blood-alcohol reading and must never be used to decide whether you are safe to drive.
| Standard drinks | Approx. hours to clear (70 kg) |
|---|---|
| 1 | 2 h |
| 2 | 4 h |
| 3 | 6 h |
| 4 | 8 h |
Why a nightcap backfires
Alcohol is a sedative, so it can help you fall asleep faster, but that is where the benefit ends. As your body clears it over the night, sleep becomes lighter and more broken, and the second half of the night in particular loses REM, the dreaming stage tied to memory and mood. Even drinking that finishes a few hours before bed can flatten deep sleep. The practical takeaways are simple: finish drinking earlier in the evening, keep the count lower, and drink water alongside. If the estimate shows alcohol still clearing well past your bedtime, the night's sleep quality is likely to suffer even if you drop off quickly. This is general wellbeing information; if alcohol or sleep is a regular problem, speak to a doctor.
Frequently asked questions
How long before bed should I stop drinking?
A common guideline is to finish at least three to four hours before bed, and longer after several drinks, so most of the alcohol has cleared. This tool estimates your own gap so you can judge it for your evening.
Does alcohol really ruin sleep if it helps me fall asleep?
Yes. It speeds falling asleep but fragments the rest of the night as it clears, cutting REM and deep sleep especially in the second half, so you wake less refreshed even after a full night in bed.
Can I use this to check if I am safe to drive?
No. This is a rough wellbeing estimate for sleep timing, not a blood-alcohol or legal measurement. Never use it to decide whether to drive; if you have been drinking, do not drive.