How to Pull an All-Nighter (And Why 90 Minutes of Sleep Beats None)

The research on staying up all night points to a simple plan: if you can spare about an hour and three quarters, sleep one full 90-minute cycle instead of going without, and use caffeine and short naps for the hours you stay awake. A driving study by Reyner and Horne found that the same 200 mg dose of caffeine kept people alert for about two hours after a short night but for only about 30 minutes after no sleep at all, which is the clearest evidence that a little sleep makes everything else work better. This guide explains what a night without sleep does, then lays out how to get through one with the least damage.

What a night without sleep does

According to the CDC, after 17 hours awake your impairment is comparable to a blood alcohol content of 0.05%, and after 24 hours it is comparable to 0.10%, above the legal driving limit in every US state.

Your own sense of how you are doing is the first thing to go. In a 1997 study at Bradley University, Pilcher and Walters gave 44 students a critical-thinking test after either a normal night or 24 hours awake. The sleep-deprived students scored significantly worse, yet rated their own concentration, effort and performance higher than the students who had slept. The authors concluded that students "are not aware of the extent to which sleep deprivation negatively affects their ability to complete cognitive tasks".

The grades follow the same pattern. Pamela Thacher of St. Lawrence University surveyed 111 students and found that two thirds had pulled at least one all-nighter in a semester, and that those who did so regularly had lower GPAs. In her words, published in Behavioral Sleep Medicine in 2008, a single night of total sleep deprivation "is not an effective practice for achieving academic goals".

An all-nighter is sometimes unavoidable, so the useful question is how much sleep your deadline still leaves room for.

The plan: keep one sleep cycle if you can

Sleep runs in cycles of roughly 90 minutes, moving from light sleep into deep sleep and REM before returning to light sleep. Waking at the end of a cycle is easier than being pulled out of deep sleep, which is what causes the heavy, confused feeling called sleep inertia. That makes the length of your sleep window matter as much as the number of hours you have left:

Time you can spare	What to do	Why
About 1 h 45 min	Sleep one full cycle	90 minutes of sleep plus about 15 minutes to fall asleep, so you wake in light sleep
About 3 h 15 min	Sleep two full cycles	Two complete cycles, including more deep sleep
30 to 60 minutes	Take a 20-minute nap instead	45 minutes often ends in deep sleep, which can leave you groggier than before
Less than 30 minutes	A caffeine nap (see below)	Combines two effects that each work for about an hour

The nap calculator works out the alarm time for any of these, including the time it usually takes you to fall asleep.

Use caffeine strategically

Caffeine works, but less well the longer you have been awake. In Reyner and Horne's 2000 study, 200 mg of caffeine (about two cups of coffee) reduced lane drifting in a driving simulator for around two hours after five hours of sleep, but for only about 30 minutes after no sleep.

A caffeine nap stretches that further. In an earlier study, the same researchers gave sleepy drivers 200 mg of caffeine followed straight away by a nap of under 15 minutes. The combination cut driving incidents to 9% of the placebo level, compared with 34% for caffeine alone, and it still worked for people who only dozed rather than fully fell asleep.

Caffeine also lingers. With an average half-life of about five hours, roughly a third of a 200 mg dose taken at 2 AM is still in your body at 10 AM, which can make a recovery nap harder; the caffeine calculator shows how much remains at any time.

Short naps during the night

Even one short nap helps. In a 1995 NASA study of long-haul airline pilots, crews who were allowed a planned rest period in the cockpit slept for an average of about 26 minutes, and the nap was associated with better alertness and performance later in the flight compared with crews who stayed awake. A 20-minute alarm keeps a nap in light sleep, so you can get back to work quickly.

The next day

The Loughborough driving studies above found sleep-related driving incidents concentrated in the early morning, with sleepiness rising again in the mid-afternoon, so the day after is when the risks are highest.

• Do not drive if you can avoid it. At 24 hours awake the CDC compares your impairment to a blood alcohol level of 0.10%.
• Take a short nap after the deadline. About 20 minutes in the early afternoon restores some alertness without making it hard to sleep that night.
• Go to bed early instead of sleeping late. Keeping your usual wake-up time helps keep one short night from shifting your whole schedule, and the sleep calculator can find a bedtime that ends on a full cycle. If the deadline cost more than one night, the sleep debt calculator shows how long it takes to catch up.

If you find yourself needing all-nighters regularly, Thacher's finding that regular all-nighters went with lower GPAs is a reason to change the routine rather than plan better nights, and the sleep schedule calculator can help move it gradually.

Conclusions

1. An all-nighter impairs you more than it feels like it does. After 24 hours awake the CDC compares impairment to a 0.10% blood alcohol level, and in Pilcher and Walters' study sleep-deprived students scored worse while rating themselves higher.
2. One 90-minute sleep cycle is the most valuable thing you can protect. Reyner and Horne found that caffeine kept people alert for about two hours after a short night versus about 30 minutes after none.
3. Caffeine naps outperform caffeine alone. Coffee followed by a nap of under 15 minutes reduced driving incidents to 9% of placebo levels, against 34% for caffeine alone.
4. Plan the recovery as well as the night. Avoid driving, keep any nap to about 20 minutes, and go to bed early the next night instead of sleeping in.