Alcohol and Sleep Calculator: When to Have Your Last Drink Before Bed

Finish your last drink at least 3 hours before bed, and longer after more than a couple: allow about 1.5 hours per standard drink (anywhere from 1 to 2, depending on how cautious you want to be) and use whichever gap is bigger. Three glasses of wine before an 11:00 PM bedtime means a last sip around 6:30 PM on the middle setting. Enter your own drinks below to see your time. This is a sleep tool only, and it never tells you whether you can drive.

How the calculator works

Your liver breaks alcohol down at a fairly steady pace. After the first few drinks its enzymes are working flat out, so drinking more does not make them go any faster ^[3]. That leaves two things that decide how much alcohol is still in you at bedtime: how much you had, and how long ago. The calculator turns that into three steps:

1. Count standard drinks. In the US, one standard drink holds about 14 grams (0.6 fl oz) of pure alcohol. That is a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot of 40% spirits ^[1]. A 16 oz pint or a generous pour of wine counts as more than one.
2. Estimate processing time. Multiply the standard drinks by the hours per drink. The default is 1.5 hours, and you can switch to 1 or 2.
3. Keep a 3-hour floor. Sleep experts suggest stopping at least 3 hours before bed ^[5], so the calculator never offers a shorter gap, even for a single drink.

Put together: latest last drink = bedtime minus whichever is larger, the processing time or 3 hours. There are no boxes for weight or sex, and you will never see a blood alcohol number. The tool answers one question only: when to stop if you care about tonight's sleep.

Why the default is 1.5 hours, not 1

You have probably heard that the body clears one drink an hour, and as a rule of thumb it is handy ^[5]. The textbook figures are a little less generous once you use the US drink size. A review of alcohol metabolism puts the average capacity of a 70 kg (154 lb) adult at about 170 to 240 grams a day, or roughly 7 to 10 grams an hour ^[2]. The review rounds that to about one drink an hour, but a US standard drink is 14 grams, and at 7 to 10 grams an hour it takes more like 1.4 to 2 hours to clear.

People also differ, sometimes by a lot. A large review of forensic studies found that blood alcohol usually falls by about 10 to 15 mg/100 mL an hour after drinking on an empty stomach and 15 to 20 after a meal, with a full range of about 10 to 35 ^[3]. So a meal in your stomach and how much you normally drink both shift the pace. The 1.5-hour default sits in the middle. Pick 2 hours if you are smaller than average, rarely drink, or simply want more margin.

Example: three glasses of wine and an 11 PM bedtime

Say you have three 5 oz glasses of 12% wine with dinner and want to be asleep by 11:00 PM. That is 3 standard drinks. At 1.5 hours each you need about 4 hours 30 minutes, so the latest last sip is 6:30 PM. On the 1-hour rule of thumb it would be 8:00 PM, and on the cautious 2-hour setting 5:00 PM. Here is how the time moves with the number of drinks on the default setting:

The gap grows fast. Five drinks would mean stopping at half past three in the afternoon, which tells you that past a certain point the number of drinks matters far more than the clock.

What alcohol at bedtime does to your night

A nightcap feels like it works, and at first it does. A review of studies in healthy sleepers found that alcohol, at every dose tested, helps you fall asleep sooner and makes the first half of the night more solid. The trouble starts later, when sleep in the second half gets lighter and more broken. Your first stretch of dreaming sleep, called REM sleep, arrives later than usual, and in most studies moderate and higher doses cut the night's total REM ^[4]. That is why a few drinks can leave you staring at the ceiling at 3 or 4 in the morning. Our guide to waking at 3 a.m. after drinking explains that rebound, and for the bigger picture, see whether alcohol helps you sleep.

A longer gap simply means more of the alcohol gets processed while you are still up and about. It won't make a drink neutral for sleep, but it does mean less alcohol on board at lights-out. If coffee is part of your evening too, the caffeine calculator does the same kind of timing for caffeine.

Limits and assumptions

This is not a driving or sobriety tool. It does not estimate blood alcohol and must never be used to decide whether you can drive, work or look after someone. Elimination rates vary widely between people ^[3], and how you feel is a poor guide.

The calculator also treats every drink as if you had it at the very end. If you sipped your way through a long evening, some of the alcohol was processed as you went, so the suggested time leans early. On the other hand, some people need a longer gap than any setting here: anyone who has several drinks quickly, drinks on an empty stomach, is especially sensitive to alcohol, is already short on sleep, or takes medicines that intensify alcohol's effects ^[5]. If you are pregnant, have liver disease or take such medicines, talk to your doctor about alcohol at all, not just its timing.

And if you find you need a drink to fall asleep, or you wake most nights after drinking, see a doctor. Drinking at bedtime to drop off and then sleeping poorly can turn into a loop of broken nights and tired days ^[5].