Naps
Why a 30 minute nap often feels worse than no nap
Thirty minutes is the length that catches people out. It is past the point where most of us start dropping into slow wave sleep and nowhere near far enough to come out the other side, so it hands you the cost of a deep nap with none of the payoff.
In short
A 30 minute nap frequently ends inside slow wave sleep, which produces the strongest sleep inertia of any nap length. That is the heavy, disoriented feeling that can take twenty minutes or more to clear, and it is why 20 minutes or a full 90 minute cycle are both better choices.
- The length to be careful with
- 30 minThe length to be careful withPast the shallow stages
- Roughly when deep sleep starts
- 25 minRoughly when deep sleep startsSooner if you are short
- Grogginess it can leave
- 20 min+Grogginess it can leaveLonger than the nap saved
The worst place to be woken is the middle
Sleep inertia is not proportional to how long you slept. It is about which stage you were in when the alarm went. Waking from a light stage produces almost nothing; waking from slow wave sleep produces the heaviest version of it, and thirty minutes is the length most likely to land you exactly there.
This is why the common experience of a half hour nap is feeling worse on waking than before lying down. The nap did work. It simply handed the benefit back later, after the inertia cleared, and by then the afternoon had moved on.
The mechanism is at /guides/what-is-sleep-inertia.
What to do instead, in either direction
If you have thirty minutes, take twenty and use the other ten to get up properly. If you have ninety, take the full cycle and come out the far side of slow wave sleep with the memory benefit included. The one thing not to do is aim at the middle.
The exception is when the goal is not alertness but recovery. If you are genuinely short on sleep and the afternoon can absorb some grogginess, thirty minutes of sleep is thirty minutes of sleep and the arithmetic changes.
Timing an alarm off sleep rather than off the clock
The reason thirty minutes is risky is that it is a clock number applied to a physiological process that does not run to the clock. Whether you are in slow wave sleep at minute thirty depends on how long you took to fall asleep and how much sleep pressure you arrived with.
An alarm that watches for a light moment rather than counting minutes sidesteps that, and it is the same mechanism Tock uses on a night alarm: watch the window, ring on a lighter patch, fall back to the set time if there is not one.
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
- More total sleep than a twenty minute nap, which matters if the goal is recovering sleep rather than feeling alert.
- A genuine benefit once the grogginess has cleared, which is usually twenty to thirty minutes after waking.
- A reasonable option when you have time to be useless for half an hour afterwards, which is rarer than it sounds.
What it costs you
- The highest chance of any common nap length of waking mid slow wave sleep, which is the worst stage to be woken from.
- Sleep inertia that can last longer than the nap itself, so the net effect on the next hour is often negative.
- Enough discharged sleep pressure to affect that night, without the memory benefit a full cycle would have bought.
Questions people ask
Is a 30 minute nap bad?
It is the riskiest of the common lengths. Thirty minutes is long enough to reach slow wave sleep and too short to get through it, so it is the nap most likely to end mid deep sleep and leave you groggier than you started. Twenty minutes or ninety are both safer.
Why do I feel terrible after a 30 minute nap?
Because you were probably woken out of slow wave sleep, which produces the strongest form of sleep inertia. It is a stage effect rather than a duration effect, and it can take twenty minutes or more to clear, which is often longer than the nap gained you.
Is 30 minutes better than 20 for a nap?
For alertness, no. Twenty is better precisely because it stops before the deep stages. Thirty is better only if your goal is recovering total sleep rather than feeling sharp afterwards, and you can afford to be groggy for a while.
Other nap lengths
Every length buys something different and costs something different.
- 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.
- 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.
- AlternativesTock vs SnoreLabSnoreLab is better if snoring is the only thing you care about and you want a remedy-tracking loop and a score you can show someone. Tock is better if you want the snoring inside a full night, with the alarm, the estimated stages and the score in one app instead of two running overnight.
- RoundupsThe best white noise apps, and when a fan beats all of themIf you want one sound forever, a hardware noise machine or a cheap fan beats every app here and costs less over two years. If you want to change what you sleep to, layer sounds together and have the same app wake you up in the morning, Tock is the better pick.
- Wake timesWaking up at 6:00amBedtimes by sleep cycle for a 6:00am alarm.
- BedtimesGoing to bed at 8:00pmWhere to put the alarm after a 8:00pm lights-out.
- Sleep by ageHow much sleep toddlers needThe American Academy of Sleep Medicine recommends that children aged 1 to 2 years sleep 11 to 14 hours per 24 hours, including naps, on a regular basis. Most of that has consolidated into the night by the second birthday, with one daytime nap doing the rest.
- Wake tonesAnnoying alarm soundsAn unbearable alarm tone works for roughly a week. After that you learn to silence it before you are properly conscious, and you are back where you started with a worse mood attached. The durable fix is not a harsher sound, it is making the alarm end somewhere your half-asleep self cannot reach.
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.