A good nap can leave you sharper for hours. A badly timed one can leave you groggy, slow and grumpy. That heavy feeling has a name: sleep inertia. The difference between the two usually comes down to how long you sleep and when. This guide explains the best nap lengths, the best time of day, and how to wake up feeling better.
In this article
The short answer
- For a quick boost, nap for 10 to 20 minutes.
- Naps of 30 to 60 minutes are more likely to leave you groggy at first.
- A 90-minute nap covers a full sleep cycle, but needs time and can affect night sleep.
- The best time is early afternoon, roughly 1 to 3 PM.
- A “coffee nap” (coffee, then a 15-minute nap) worked best in a driving study.
What sleep inertia is
Sleep inertia is the groggy, confused feeling right after waking. Your brain does not switch on all at once. For a short time, your reaction speed, memory and decision-making are worse than normal. In a 2006 study, people’s thinking skills in the first minutes after waking were worse than after a full night without sleep. The effect usually fades within 15 to 30 minutes, but it can last longer.
Sleep inertia is strongest when you wake from deep sleep. That is why nap length matters so much.
Why nap length matters
When you fall asleep, you move through light sleep first, then into deep sleep, usually after about 20 to 30 minutes. A full cycle, including dream (REM) sleep, takes around 90 minutes. If your alarm goes off in the middle of deep sleep, you are more likely to wake up groggy.
In a 2006 study, adults who had slept only 5 hours took naps of 5, 10, 20 or 30 minutes at 3 PM:
- 5 minutes did very little.
- 10 minutes improved alertness and mood straight away, and some benefits lasted over 2 hours.
- 20 minutes helped too, but the benefits took about half an hour to appear.
- 30 minutes first caused grogginess, and the benefits came later.
A 2017 review found that even naps of 30 minutes or less sometimes cause sleep inertia, especially if you are very short on sleep or nap at night. So shorter is safer when you need to be sharp straight away.
The nap lengths, compared
| Nap length | Good for | Grogginess risk |
|---|---|---|
| 10 to 20 minutes | A quick lift in alertness and mood | Low |
| 30 to 60 minutes | Some memory benefits, if you have time to wake up properly | Higher |
| About 90 minutes | A full cycle, useful after a very short night or before a night shift | Lower, if you wake at the end of the cycle |
The best time to nap
For most people, the best window is early afternoon, roughly 1 to 3 PM. Many people have a natural dip in alertness then, so it is easier to fall asleep. Napping later in the day reduces your “sleep pressure” and can make it harder to fall asleep at night.
If you work nights, the timing is different. A nap before your shift, and sometimes a short one during a break, can help. See our night shift guide for details.
The coffee nap
Caffeine takes about 20 to 30 minutes to start working. A coffee nap uses that delay: drink a cup of coffee, then nap straight away for about 15 minutes. You wake up just as the caffeine starts to work.
In a 1997 study, sleepy drivers in a simulator had far fewer driving incidents after a coffee plus a short nap than after coffee alone. Even people who only dozed lightly benefited. Avoid coffee naps late in the day, as caffeine can disturb sleep many hours later.
Tips for a better nap
- Set an alarm for your nap length plus about 5 minutes to fall asleep.
- Make it dark and quiet. An eye mask and earplugs help.
- Lie down or recline if you can. Sleeping upright is lighter and less restful.
- After waking, get light and move. Bright light, cold water on your face or a short walk help clear grogginess.
- Do not use the snooze button. Drifting back to sleep can make you groggier.
- Keep it regular. People who nap often seem to get more benefit and less grogginess from naps.
Pilots and planned naps
In a NASA study from 1994, long-haul pilots were allowed a planned 40-minute rest in the cockpit while a colleague flew. They fell asleep in about 6 minutes and slept about 26 minutes. Compared with pilots who did not rest, they were more alert later in the flight, including during descent and landing. Aviation regulators in many countries now allow this kind of planned rest, though the US does not.
Myth vs fact
Myth: A longer nap is always better. Fact: Naps of 30 to 60 minutes often leave you feeling worse at first. Large studies also link regular naps of an hour or more with poorer health, possibly because they are a sign of poor night sleep.
Who should avoid naps
If you have insomnia, naps can make it harder to sleep at night. Treatment for insomnia usually asks you to avoid them. If you need a nap every day even after a full night’s sleep, that is worth discussing with a doctor.
When to see a doctor
Strong sleepiness every day, falling asleep without meaning to, or long naps that never feel refreshing can be signs of sleep apnea, narcolepsy or another condition. See a doctor, especially if you snore loudly or feel sleepy while driving.
Frequently Asked Questions
Is a 20-minute nap better than a 1-hour nap?
For a quick boost, yes. A 20-minute nap is less likely to leave you groggy. A 1-hour nap may help memory more, but you need time to wake up fully afterwards.
How do I stop feeling groggy after a nap?
Keep naps short, get up straight away, and go into bright light. A glass of cold water or a short walk also helps. The feeling usually passes within 15 to 30 minutes.
What if I cannot fall asleep during a nap?
Resting quietly with your eyes closed is still restful. If you have not fallen asleep after 15 minutes, get up and carry on with your day.
Can naps replace night sleep?
No. Naps can top up a short night, but they do not replace the deep and dream sleep you get from a full night. Adults still need 7 hours or more in total. Read why adults need at least 7 hours.
Is it normal to dream during a short nap?
It can happen, especially if you are short on sleep, because your body may go into dream sleep faster. Frequent dreaming within minutes of falling asleep, together with strong daytime sleepiness, is worth mentioning to a doctor.
Conclusion
The best nap for most people is short and early: 10 to 20 minutes, in the early afternoon, with an alarm. If you have more time, a full 90-minute cycle can work too. Avoid the middle lengths when you need to be sharp straight away, and if you feel the need to nap every day, look at your night sleep first. Our guide to biphasic sleep covers planned daily naps in more detail.
Sources
- Brooks A, Lack L. A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? Sleep, 2006.
- Hilditch CJ, et al. A review of short naps and sleep inertia: do naps of 30 min or less really avoid sleep inertia and slow-wave sleep? Sleep Med, 2017.
- Tassi P, Muzet A. Sleep inertia. Sleep Med Rev, 2000.
- Wertz AT, et al. Effects of sleep inertia on cognition. JAMA, 2006.
- Reyner LA, Horne JA. Suppression of sleepiness in drivers: combination of caffeine with a short nap. Psychophysiology, 1997.
- Milner CE, Cote KA. Benefits of napping in healthy adults: impact of nap length, time of day, age, and experience with napping. J Sleep Res, 2009.
- Yamada T, et al. Daytime napping and the risk of cardiovascular disease and all-cause mortality. Sleep, 2015.
- Rosekind MR, et al. Crew factors in flight operations IX: effects of planned cockpit rest on crew performance and alertness in long-haul operations. NASA, 1994.
