Naps
The 90 minute nap, and why the length is not arbitrary
Ninety minutes is roughly one complete sleep cycle. That is the whole reason it is the recommended long nap: you go down through the deep stages and come back up through REM, so the alarm finds you near the surface rather than at the bottom.
In short
A 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.
- One average sleep cycle
- 90 minOne average sleep cycleReal ones run 70 to 120
- The stage it ends in
- LightThe stage it ends inWhy the wake-up is clean
- Deep sleep and REM included
- BothDeep sleep and REM includedShorter naps get neither
The number comes from the cycle, not from convenience
Most nap advice gives you a duration and leaves you to trust it. This one has a mechanism behind it that is worth knowing, because it also tells you when the advice will fail. Sleep runs in cycles of roughly ninety minutes, descending through light sleep into slow wave and then rising into REM before starting again. Wake at the end of one and you are near the surface. Wake in the middle and you are not.
So the ninety minute nap is not ninety minutes because ninety is a nice number. It is ninety because that is roughly where the cycle puts you back within reach of the surface, and the whole benefit of the length is that timing.
Where the average breaks down
Real cycles run anywhere from about seventy to a hundred and twenty minutes, and they change length through a night. A ninety minute nap is therefore a good bet rather than a guarantee: some people will surface at seventy five and some will still be deep at ninety five.
That variability is exactly the problem a smart alarm exists to solve, and it applies to a nap as much as to a night. Watching for a lighter moment inside a window beats counting to a number that was only ever an average.
How that window works on a night alarm: /features/smart-wake.
The cost is real and worth stating
A ninety minute nap discharges a lot of sleep pressure. For somebody who sleeps well, that is the single most likely thing on this site to make falling asleep at night harder, and taking one at five in the afternoon is close to guaranteeing a late bedtime.
The version that works is early and occasional: an afternoon nap after a genuinely short night, rather than a daily habit layered on top of adequate sleep.
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
- A complete cycle, including both the slow wave sleep associated with physical recovery and the REM associated with some kinds of memory and emotional processing.
- A relatively clean wake-up, because the cycle brings you back toward the surface before it ends.
- The largest reduction in sleep pressure of any nap on this list, which is what makes it the real recovery option.
What it costs you
- An hour and a half, which is the actual barrier rather than anything physiological.
- A substantial dent in that night sleep pressure, so it is the nap most likely to push your bedtime later.
- Ninety minutes is an average and your cycle may not match it, so the clean exit is likely rather than guaranteed.
Questions people ask
Why is 90 minutes the recommended nap length?
Because it is roughly one full sleep cycle. You descend through deep sleep and rise back through REM, so the nap ends in a lighter stage and the wake-up is much cleaner than from a 30 or 60 minute nap that stops in the middle.
Is a 90 minute nap better than a 20 minute one?
They do different jobs. Twenty minutes is for alertness in the next few hours and costs almost nothing. Ninety is for recovery and includes deep sleep and REM, and it costs an hour and a half plus a real effect on that night. Neither is better in the abstract.
Will a 90 minute nap keep me up at night?
It is the most likely of any nap length to. Ninety minutes of sleep is ninety minutes of sleep pressure discharged, and that has to come from somewhere. Early afternoon reduces the effect considerably; late afternoon or evening more or less guarantees it.
Other nap lengths
Every length buys something different and costs something different.
- The 60 minute napA 60 minute nap includes a substantial amount of slow wave sleep, which is useful for recovery and for some kinds of memory, and it usually ends before the cycle completes. That means the benefit is real and the wake-up is often groggy, so it suits situations where the hour afterwards is flexible.
- The 20 minute napA 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.
Elsewhere on the site
A different corner of the same problem.
- Head to headSleep Cycle vs SnoreLabIf someone in the bed has complained about your snoring and you want to test whether anything helps, SnoreLab. If you want a picture of the whole night and an alarm at the end of it, Sleep Cycle.
- FeaturesSmart wakeSmart wake is a 30 minute window before your alarm in which Tock watches for a lighter moment in your sleep and rings as soon as it finds one. If it never finds one, your alarm goes off at the exact time you set.
- Sleep soundsFireplaceA fire is a soft broadband roar with sparse, sharp crackles laid on top, and those crackles are transients, precisely the kind of sudden sound a light sleeper surfaces for. It is one of the best wind-down sounds in the library and one of the weakest choices to leave running until morning.
- Tock for youRotating shift nursesYour rota moves you from days to nights and back again, sometimes inside the same week, and there is no schedule to settle into because the schedule keeps changing. Every adjustment gets interrupted by the next one.
- AlternativesTock vs PzizzKeep Pzizz if you nap, or if your mind needs words to hold onto while you fall asleep. Tock generates its sound too, but it has no voiceover and nothing for naps. What Tock adds is the alarm, the tracking and the morning report Pzizz does not attempt.
- RoundupsThe best sleep trackers that don't need a watchTock is the best sleep tracker without a watch. Leave the phone on the nightstand and it uses the microphone and accelerometer all night, classifies snores, coughs and sleep talking on device, and hands you a report plus the audio in the morning. SleepScore is the strongest alternative if you would rather nothing listened to the room.
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.