How long should a power nap be?

The short answer

For a quick boost, aim for 10 to 20 minutes of sleep, and set your timer a few minutes longer than that to allow for drifting off. Much longer, and you are more likely to wake up groggy. Much shorter, and you may not get much out of it.

Advice varies a little. Mayo Clinic currently calls a 20- to 30-minute nap ideal, while one of the best-known experiments on nap length found that ten minutes of sleep worked best. Everyone agrees on the direction, though: the longer you nap, the more likely you are to feel groggy afterwards.

Why long naps leave you groggy

That heavy, foggy feeling after waking has a name: sleep inertia. The longer you sleep, the further you tend to sink into deep sleep, and waking from deep sleep is what tends to leave you slow and muddled for a while. Mayo Clinic notes that the grogginess often goes away within about 35 minutes.

A short nap mostly keeps you in lighter sleep, so you surface more easily. That is the whole idea of a power nap: some of the benefit of sleep, without paying for it in grogginess.

What the research says about nap length

In a 2006 study in the journal Sleep, researchers at Flinders University in Australia limited 24 healthy young adults to about five hours of sleep, then gave them an afternoon nap of exactly 5, 10, 20 or 30 minutes of sleep, or no nap at all. The 10-minute nap improved alertness and performance straight away, and some of the benefits lasted around two and a half hours.

The 20-minute nap helped too, but its benefits took about half an hour to appear. The 30-minute nap left people groggy at first before they improved, and the 5-minute nap did very little. Those were minutes of actual sleep. Most people take several minutes to drop off, which is why a 20-minute nap usually needs nearer 25 minutes lying down.

What NASA's pilot study actually found

You may have read that NASA found the perfect nap lasts 26 minutes. That is not quite what happened. In a study published in 1994, NASA and the US Federal Aviation Administration gave long-haul airline pilots a planned 40-minute rest opportunity on the flight deck during the quiet cruise part of the flight, one pilot at a time while the others flew. The pilots who rested fell asleep in under six minutes on average and slept for about 26 minutes.

Compared with pilots who kept flying, they held their reaction times steadier across the trip, and in the last 90 minutes of the flight, through descent and landing, they showed fewer of the brief brain-wave and eye-movement signs of drowsiness. So 26 minutes was simply how long they slept, not a recommendation. The procedure also gave each pilot time to come round before taking up their duties again.

When and where to nap

Timing and setting matter almost as much as length:

• Early afternoon is the natural window. Many people get sleepy in the mid-afternoon, and Mayo Clinic warns that napping after 3 p.m. can make it harder to sleep at night.
• Find somewhere quiet and dark, at a comfortable temperature, and keep your phone out of reach or face down.
• Lie down if you can. A reclining chair works too.
• Set a timer, so you can let go without one eye on the clock.
• If you do not fall asleep, that is fine. Resting quietly with your eyes closed is still a break.
• Give yourself a few minutes after waking before anything that needs a clear head, like driving.

When a nap is not the answer

A nap takes the edge off tiredness, but it does not replace a night's sleep. The pilots in NASA's study still built up a sleep debt over their trip, and the cockpit nap did not change it. If you find you rely on a nap to get through every afternoon, look at your nights first.

Napping is not for everyone, either. If you have trouble falling or staying asleep at night, Mayo Clinic notes that daytime naps can make it worse. And if you are exhausted however much you sleep, or suddenly find you need far more naps than usual, that is worth raising with a doctor rather than solving with a timer.

Using the Power Nap timer

The Power Nap timer puts a 20-minute nap inside a 25-minute session: a minute to lie down and turn the phone face down, two minutes to let your breathing slow, the nap itself, then two minutes of gentle waking. A soft chime and a calm voice bring you back and tell you when to sit up, and the session ends quietly, without an alarm.

On a phone, a web page can stop running when the screen locks, so the timer asks your browser to keep the screen on while it runs. Leave the phone face down, and plug it in if the battery is low. The Timer AI iPhone app keeps going on the Lock Screen instead. For a shorter rest, Calm City Nap runs for 20 minutes in all, with 15 of them for resting.