Naps
The 20 minute nap, and why everyone recommends it
Twenty minutes is the nap length almost every piece of advice lands on, and unusually the popular answer is the right one. It sits in the widest gap between getting a real benefit and paying for it on the way out.
In short
A 20 minute nap is the standard recommendation because it produces a solid alertness benefit while ending before most people reach slow wave sleep, so you wake up clear rather than groggy. It is long enough to be worth the time and short enough to stay safe.
- Asleep, not in bed
- 20 minAsleep, not in bedSet the timer for 25 to 30
- Roughly when deep sleep starts
- 25 minRoughly when deep sleep startsVaries by person and debt
- Rough duration of the lift
- 2 to 3 hRough duration of the liftLonger than a 10 minute nap
Why twenty and not fifteen or twenty five
The number is a compromise between two curves running in opposite directions. The benefit of a nap rises with its length. The cost of waking from it rises too, but not smoothly: it stays near zero and then climbs sharply once you enter slow wave sleep, which for most people is somewhere after about twenty five minutes.
Twenty sits just under that cliff. It captures nearly all of the benefit available in the shallow stages and almost none of the penalty, which is why it survives as advice despite being suspiciously round.
The exception is when you are already short
Sleep pressure changes the timetable. Somebody who slept five hours last night reaches the deeper stages faster than somebody who slept eight, which means the same twenty minute nap can end inside slow wave sleep rather than before it, and the wake-up is correspondingly worse.
The practical version: if a twenty minute nap consistently leaves you groggy, you are probably not napping wrong, you are probably short on sleep at night. The nap is reporting the debt rather than causing it.
What that debt is and whether it can be repaid: /glossary/sleep-debt.
Set the timer longer than the nap
Twenty minutes means twenty minutes asleep. Almost nobody falls asleep the instant they lie down, so a twenty minute timer usually delivers twelve to fifteen minutes of sleep. Setting twenty five or thirty and letting the settling time be part of it is the version that matches the advice.
This is where an alarm that watches rather than counts is genuinely useful, because the thing you actually want is twenty minutes after you fall asleep, and only the phone knows when that was.
What it buys and what it costs
Every nap length is a trade. These are both sides of this one, at the same size.
What it gives you
- The largest alertness benefit available without entering slow wave sleep, which is what makes it the default recommendation.
- A clean wake-up for most people, because twenty minutes usually ends just before the deep stages begin.
- Enough of a lift to carry an afternoon, rather than the short bridge a ten minute nap provides.
What it costs you
- Nothing for memory consolidation, which needs a full cycle rather than a fragment of one.
- It can tip into deep sleep if you are heavily sleep deprived, because the deeper stages arrive sooner when the pressure is high.
- Taken late in the day it will discharge enough sleep pressure to make falling asleep at night harder.
Questions people ask
Is 20 minutes the best nap length?
For an afternoon alertness boost, yes for most people. It captures nearly all the benefit available before slow wave sleep begins and almost none of the grogginess that comes from being woken out of it. For memory consolidation, a full 90 minute cycle is the better nap.
Why do I wake up groggy from a 20 minute nap?
Usually because you are short on sleep at night. High sleep pressure means you reach the deeper stages faster, so a twenty minute nap that would normally end before slow wave sleep ends inside it instead. The nap is reporting the debt rather than causing it.
When should I take a 20 minute nap?
Early afternoon, roughly in the dip most people feel some hours after waking. Later than about eight hours before your bedtime it starts eating the sleep pressure you need for that night, which makes falling asleep harder.
Other nap lengths
Every length buys something different and costs something different.
- The 10 minute napA 10 minute nap lifts alertness without taking you into slow wave sleep, so you wake up clear rather than groggy. It is the safest nap to take close to work or driving, and it does nothing for memory consolidation, which needs considerably longer.
- The 90 minute napA 90 minute nap is approximately one full sleep cycle, which means it ends in a lighter stage rather than in slow wave sleep. That produces much less grogginess than a 30 or 60 minute nap, and it includes both the deep sleep and the REM that shorter naps miss.
Elsewhere on the site
A different corner of the same problem.
- Wake tonesNature alarm soundsBirds, water and weather make calm wake tones and carry one specific failure: a natural sound is easy for a sleeping brain to fold into a dream rather than treat as an alarm. Tock counters that in two places, by scheduling the alarm through Apple's AlarmKit so it lands on the system full-screen alert, and by keeping it ringing until a wake-up mission is done.
- Head to headHeadspace Sleep vs PzizzIf you nap in the afternoon, or you get bored hearing the same track night after night, Pzizz. If you want to be taught how to wind down and to still be doing it in three months, Headspace Sleep.
- FeaturesAlarm on silentTock's alarms are registered with iOS through Apple's AlarmKit framework rather than played by the app in the background. That is why they ring with the ringer off, through a Focus, with Tock closed, on the native full-screen alert.
- Sleep soundsNight forestA night forest bed is a soft, broad rustle of leaves with occasional distant events layered into it, and the design rule that makes it work is that none of those events should ever be identifiable. A sound you can name is a sound you then lie there waiting to hear again, which is the exact opposite of falling asleep.
- Tock for youTravellers with jet lagYou landed, you are on local time on paper, and your body is running four or eight hours behind. Wide awake at 3am, unusable at 3pm, and it lasts roughly a day per time zone.
- AlternativesTock vs Sleep CycleSwitch to Tock if you want the alarm itself to be different: a system alarm that rings on silent and through a Focus, moved up to 30 minutes earlier into a lighter moment, with a task before it stops. Stay with Sleep Cycle if you have years of history in it, or if someone in the house is on Android.
A nap alarm that watches instead of counting
Whether you are in deep sleep at minute thirty depends on how fast you dropped off and how short last night was. Tock watches for a lighter moment rather than trusting the clock.