How long should a nap be? Power nap vs. full cycle

There are two good nap lengths and one awkward one in between. The good ones are about 20 minutes and about 90 minutes. The awkward one is around 45 minutes.

The short nap: about 20 minutes

The National Sleep Foundation (NSF) is direct: "Researchers say a 20 minute nap is the best length."

The CDC's National Institute for Occupational Safety and Health (NIOSH) says the same for daytime schedules. In its training course for nurses, it recommends a brief nap of under 20 minutes, with an alarm set for 15 to 30 minutes. It adds two useful points:

• A brief nap can improve alertness for a couple of hours with less grogginess.
• It "does not disrupt subsequent sleep at night because it does not reduce the homeostatic buildup of pressure for sleep."

In plain terms, a short nap takes the edge off without spending the sleepiness you need for bedtime.

The long nap: about 90 minutes

NIOSH notes that waking after about 90 minutes, "predicted to be the end of a sleep cycle," may mean less grogginess, and that it clears faster. The NSF says napping for 60 to 90 minutes is enough time to have deep, slow-wave sleep.

Ninety minutes works because it lines up with one average sleep cycle. The 90-minute cycle guide explains why that number is only an average.

The awkward middle: around 45 minutes

The NSF warns that "medium-length naps of around 45 minutes can be problematic." NIOSH explains why: sleep gets deeper the longer you sleep, reaching deep sleep at about 1 hour. Waking from deep sleep can cause sleep inertia, a groggy, slow feeling. With a 20- or 90-minute nap, NIOSH says grogginess may go away more quickly, within 15 to 30 minutes.

Our nap calculator shades 30 to 60 minutes of sleep as the zone to avoid.

How to set the alarm

The alarm has to cover the time it takes to fall asleep, not just the nap. Many people drift off faster for a nap than at night, so the calculator's default is 10 minutes. Change it to your own number.

Formula: alarm = time you lie down + minutes to fall asleep + nap length.

Here are two worked examples from our library:

Lie down	To fall asleep	Power nap alarm (20 min)	Avoid waking	Full cycle alarm (90 min)
1:30 PM (13:30)	10 min	2:00 PM (14:00)	2:10–2:40 PM	3:10 PM (15:10)
12:45 PM (12:45)	5 min	1:10 PM (13:10)	1:20–1:50 PM	2:20 PM (14:20)

Take the first row. You lie down at 1:30 PM and fall asleep around 1:40. A 2:00 PM alarm gives 20 minutes of sleep, 30 minutes in total. A 3:10 PM alarm gives one full 90-minute cycle. Waking between 2:10 and 2:40 PM would mean 30 to 60 minutes of sleep, the groggy middle.

Note that the 2:00 PM alarm fits NIOSH's advice to set the alarm for 15 to 30 minutes: it rings 30 minutes after you lie down.

When to nap

The NSF says most sleep researchers recommend napping before 2 p.m., so the nap has less impact on your night. That is why the nap calculator shows a note for naps that start at 2 PM or later.

Shift workers are the big exception. For someone who works nights, a long afternoon nap before the shift can be the point. NIOSH describes studies where nurses napped from 3:30 to 5:00 PM before a night shift. See our shift-work guide.

Coffee before a nap?

The NSF mentions that drinking a small amount of caffeine before a nap may help you avoid the groggy feeling of sleep inertia. If you try it, keep the clock in mind. CDC lists avoiding caffeine in the afternoon or evening among its healthy sleep habits. The caffeine timing guide shows why late caffeine reaches into the night.

Do you need to nap at all?

Not necessarily. The NSF notes that healthy adults don't need to nap. If naps leave you groggy or keep you up at night, you may simply not be someone who benefits from them.

There is one more caution from NIOSH. If you are very sleep deprived, your brain may reach deep sleep sooner, so even a short nap can leave you groggy for longer. And if you need naps just to get through ordinary days, that is worth raising with a doctor. NINDS advises seeing one if you feel unusually tired during the day.