Short answer: some sleep is almost always better than none, but the length matters. If you only have a couple of hours, sleep for 90 minutes (one full cycle) or 20 minutes (a power nap). A 30 to 60 minute sleep is the one to avoid, because you're likely to wake up in deep sleep and feel worse than if you'd stayed up.
Free toolNap CalculatorWhen to set your alarm for a power nap or a full-cycle nap.Why any sleep helps
Being awake for a long stretch impairs you in a way that's easy to underestimate. In a classic 1997 study, people kept awake for 17 hours performed about as poorly as people at a blood alcohol level of 0.05%. After 24 hours awake, it was comparable to 0.10%, above the legal driving limit in the US.
Even a short sleep takes the edge off that. Your brain gets a chance to clear some of the pressure that builds while you're awake.
The problem with 1 hour
The catch is sleep inertia: the heavy, confused, slow feeling when you wake up from deep sleep. It can last from a few minutes to half an hour or more.
Deep sleep usually arrives around 20 to 30 minutes after you nod off and dominates the first cycle. An alarm at the 60-minute mark has a good chance of catching you right in it. That's why a one-hour sleep so often feels awful.
How long should you sleep?
| Time you have | What to do |
|---|---|
| Under 45 minutes | 20-minute power nap |
| About 2 hours | One full cycle: 90 minutes of sleep |
| 3.5 hours or more | Two cycles: 3 hours of sleep |
| 5 hours or more | Three cycles: 4.5 hours of sleep |
Add the time it takes you to fall asleep, usually 10 to 15 minutes. The nap calculator does this for you, and for longer stretches the sleep calculator's "Sleep now" button gives you wake-up times that land at the end of a cycle.
Quick chart: you have to be up at 6 AM
Here's what to do depending on when you can finally lie down. Each alarm time includes about 15 minutes to fall asleep (10 for the power nap).
| Lying down at | Best option | Set your alarm for |
|---|---|---|
| 1:00 AM | 3 cycles (4.5 hours) | 5:45 AM |
| 2:00 AM | 2 cycles (3 hours) | 5:15 AM |
| 3:00 AM | 1 cycle (90 minutes) | 4:45 AM |
| 4:00 AM | 1 cycle (90 minutes) | 5:45 AM |
| 5:00 AM | 20-minute power nap | 5:30 AM |
Notice the 3:00 AM row: the alarm goes off at 4:45, over an hour before you need to be up. That's on purpose. Waking at the end of one cycle usually beats sleeping on into the middle of the next.
When staying up might make sense
- You're very likely to sleep through your alarm. If missing a flight or an exam is a real risk, the safest plan might be staying up and napping afterwards. Set two alarms if you do sleep.
- You have less than 20 minutes. Just rest with your eyes closed.
If you pull an all-nighter anyway
- Don't drive. Drowsy driving is dangerous, and you won't be a good judge of how impaired you are.
- Use caffeine early, not late. A coffee in the morning helps. One in the late afternoon will wreck your recovery sleep. Find your cutoff.
- Get bright light in the morning. It helps you feel more alert and keeps your body clock on track.
- Go to bed at a normal time that night, or a little early. Sleeping until noon the next day shifts your body clock and makes the following night harder.
For a full plan for the day after, see how to recover from an all-nighter.
Short sleep is a rescue, not a routine
A 90-minute sleep before a flight gets you through the morning. It doesn't replace a night. If you're regularly cutting sleep this short, you're building sleep debt that shows up in focus, mood and reaction time long before you feel it. Watch for the signs you're sleep deprived.