Nap calculator
You are not bad at napping, you picked the wrong length
Stop before deep sleep starts, or go all the way through a cycle and come back up. The stretch in between is the one that leaves you worse off than when you lay down.
Set the alarm for
Every time below already includes the 10m you said it takes you to drop off, so it is the time to put on the clock, not the time to close your eyes.
- 2:20 pmThe short one, 10m asleeplight sleep only
- 2:30 pmThe power nap, 20m asleepthe usual advice
- 2:40 pmThe edge of it, 30m asleepgrogginess likely
- 3:10 pmThe heavy one, 1h asleepgrogginess likely
- 3:40 pmA full cycle, 1h 30m asleepcomes back up
Nothing here is a prescription. How long you need, and how rough the first few minutes feel, depends on how much sleep you are already short and how late in the day it is. A nap after about four in the afternoon can start eating into the pressure to sleep that night.
Why 30 to 60 minutes is the awkward window
Somewhere past twenty minutes you slide into slow-wave sleep, the heaviest stage there is. Waking out of it is what people mean by nap grogginess: sleep inertia, which usually clears in fifteen to thirty minutes but can hang around longer. Nothing has gone wrong. You just got interrupted at the deepest point. Either stop before you get there, or go all the way round and come back up.
About that coffee
Caffeine takes roughly twenty to forty-five minutes to reach its peak, which is why people drink one immediately before a twenty minute nap and wake up as it lands. It also leaves slowly: about half of a dose is still in a typical adult five hours later, though that varies a lot between people. A 2013 study in the Journal of Clinical Sleep Medicine found caffeine six hours before bed still measurably cut sleep. Six hours before your usual bedtime is a reasonable place to draw your own line.
What is happening in there
A nap is a cycle you either duck out of or finish
Sleep runs in laps. You start in light sleep, sink into slow-wave sleep, come back up through REM and surface. The whole trip takes most people somewhere around ninety minutes, and where a nap lands you on that curve decides everything about how the next hour feels.
For the first twenty minutes or so you are still in light sleep. Waking there is easy: you get the alertness a nap is for and almost none of the cost. Past that you slide into the heaviest stage of the night, and being pulled out of it produces sleep inertia, which is the thick, slow, slightly annoyed feeling people describe as feeling worse after the nap. It usually clears in fifteen to thirty minutes, but that is fifteen to thirty minutes you did not plan for.
Around ninety minutes you have come back round to light sleep again, which is why a full cycle can feel fine even though it is four times as long as a power nap. Anything between those two points is the awkward middle.
Why the numbers here are approximate
How fast you reach deep sleep depends on how much sleep you already owe. Somebody who slept five hours last night gets there sooner than somebody who slept eight, so the same thirty minute nap is a light doze for one person and a hole for the other. The lengths above are a sensible default, not a rule about your body.
The same problem exists at night, at a much larger scale, which is what Tock is for. It watches the last half hour before your alarm for a lighter moment and rings then, so the morning does not depend on a lucky guess about where you were in a cycle.
Questions
What people ask about napping
How long should a nap be?
Ten to twenty minutes for most purposes. That keeps you in light sleep, so you get the lift in alertness without the fog that comes from being woken out of deep sleep. If you are properly short on sleep and have the time, about ninety minutes lets you finish a whole cycle and surface near the light end of it.
Why do I feel terrible after a 45 minute nap?
Because somewhere past twenty minutes you drop into slow-wave sleep, the heaviest stage there is, and forty-five minutes wakes you in the middle of it. The heavy, disoriented feeling is sleep inertia. It usually clears in fifteen to thirty minutes and it is not a sign that anything is wrong, just that the alarm landed at the deepest point.
Is a 30 minute nap too long?
Thirty minutes sits right on the edge. Some people are fine, some wake up groggy, and which of those you are depends mostly on how sleep-deprived you already were, because the more you owe, the faster you drop into deep sleep. If thirty minutes reliably leaves you foggy, twenty is the safer number.
Should I drink coffee before a nap?
Caffeine takes roughly twenty to forty-five minutes to peak, so drinking one immediately before a twenty minute nap means you wake up as it arrives. The evidence for the combination beating either on its own is limited, but the timing is real and it costs nothing to try.
What time is too late to nap?
Napping late in the afternoon eats into the sleep pressure you have been building all day, which is what makes you drowsy at bedtime. As a rough line, keep naps before about four in the afternoon if you struggle to fall asleep at night. If you sleep fine, a later nap matters much less.
How late can I have caffeine before bed?
About half of a dose is still in a typical adult five hours later, though that varies a lot between people. A 2013 study in the Journal of Clinical Sleep Medicine found caffeine taken six hours before bed still measurably reduced sleep. Six hours before your usual bedtime is a reasonable place to draw your own line.
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