If you hit a slump in the afternoon, especially after a short night, a nap can help. The US National Heart, Lung, and Blood Institute (NHLBI) notes that napping during the day may boost your alertness and performance.1 But length matters. Get it right and you wake up sharper. Get it wrong and you wake up groggy, or lie awake that night.
Here's what the research says about how long to nap, when to do it, the viral "coffee nap" and "NASA nap," and who's better off skipping naps.
The short answer
For most adults, a nap of 10 to 20 minutes in the early afternoon is the safe bet. The NHLBI advises adults to nap for no more than 20 minutes, and to limit naps or take them earlier in the afternoon if they have trouble falling asleep at night.1
Longer naps can still be useful, but they come with trade-offs:
- 10–20 minutes: a quick lift in alertness with little grogginess.
- About 30 minutes: may help you take in new information, but expect a groggy spell first.
- 60–90 minutes: a deeper sleep and more grogginess on waking. Mainly worth it after a very short night.
What the studies found
10 minutes: the quick fix
In one study, 24 healthy young adults slept only about 5 hours, then took a nap at 3 pm the next afternoon. A 5-minute nap did little. A 10-minute nap improved sleepiness, fatigue, vigour and mental performance straight away, with some benefits lasting up to about 2.5 hours. After a 20-minute nap, the benefits appeared about 35 minutes later. After 30 minutes, people were groggy and performed worse at first, then improved. The researchers concluded that 10 minutes was the most effective nap length they tested.2
Those times were minutes of actual sleep, so allow a few extra minutes to drift off.
30 minutes: more benefit, more grogginess
A 2023 study in Singapore compared 10-, 30- and 60-minute naps in 32 young adults who usually spent only 6 to 6.5 hours in bed at night. All three naps lifted mood and reduced sleepiness, although the mood boost from the 10-minute nap faded within an hour. Only the 30-minute nap improved memory encoding, meaning how well people took in new information afterwards. The 30- and 60-minute naps caused some grogginess, but it wore off within 30 minutes.3
The authors found no clear "winning" length, but said a 30-minute nap seemed to offer the best trade-off. Allowing 10–15 minutes to fall asleep, they suggested setting aside about 40–45 minutes to get 30 minutes of sleep.3
Why longer naps leave you groggy
That foggy, slow feeling after waking is called sleep inertia: a temporary spell of sleepiness, disorientation and poorer performance. Its strongest effects happen in the first 30 minutes after waking. Longer naps contain more deep sleep, and the grogginess tends to be worse. A 2019 review advised keeping naps under 30 minutes if you need to be alert soon after waking.4
What about a 90-minute nap?
Long naps have a following among athletes. A 2021 systematic review of 18 studies in physically active people and athletes found that most showed a benefit from napping: better short-term physical performance (such as jumping, strength and repeated sprints), endurance, reaction time and attention. Longer nap opportunities of about 90 minutes produced bigger improvements and less fatigue, and the authors suggested 90 minutes for athletes who are chronically short of sleep. They also cautioned that the quality of the evidence is limited.5
So a long nap can be a recovery tool after a short night, especially before a training session later in the day. Leave time to shake off the grogginess before you train, and don't make long naps a daily habit (see below).
When to nap
The lab studies in this article scheduled naps between about 12:40 and 3 pm. In practice, nap soon after lunch rather than late in the day, especially if you have trouble sleeping at night.1
Trend check: the coffee nap
A "coffee nap" means drinking coffee right before a short nap. The idea is that the caffeine kicks in around the time you wake up. In a small Japanese study, 10 young adults tried different ways to beat early-afternoon sleepiness. Taking 200 mg of caffeine just before a 20-minute nap at 12:40 worked best: it reduced sleepiness and improved performance for the whole hour of testing that followed. Bright light right after the nap was about as good for sleepiness, though not for performance, and washing the face gave a short-lived boost.6
A review of sleep inertia also found that caffeine taken before a short nap can ease grogginess on waking.4 If you want to try it, have your coffee, lie down straight away and set an alarm for 20 minutes. Keep coffee naps to the early afternoon, because the effects of caffeine can last up to 8 hours.1
Trend check: the "NASA nap"
The "NASA nap" comes from a 1994 NASA study of long-haul airline pilots. During the quiet cruise phase of the flight, one group had a planned 40-minute rest period in the cockpit. They fell asleep on 93% of these opportunities, took about 6 minutes to drop off and slept for about 26 minutes on average. Compared with pilots who had no rest period, they showed better alertness and performance, and the benefits lasted through descent and landing.7
So the famous "26-minute nap" is how long the pilots happened to sleep in a 40-minute window, not a length the study compared with others. It fits the wider research: a short nap, taken when you're tired, helps.
Is napping good for you?
Short naps look fine. Long daily naps are a different story. A 2015 meta-analysis of 11 long-term studies with more than 150,000 people found that napping for an hour or more a day was linked to an 82% higher risk of cardiovascular disease and a 27% higher risk of dying during the studies, compared with not napping. Naps of less than an hour a day weren't linked to either. For cardiovascular disease, risk dipped slightly up to about 30 minutes a day, then rose with longer naps.8
These were observational studies, so they can't show that long naps cause harm. The authors pointed out that people who take long naps may already be unwell, or may be napping because of poor night-time sleep, for example from sleep apnoea.8 The practical message: a short nap is a reasonable tool, but needing a long nap every day is worth paying attention to.
Who should skip the nap
- People who struggle to sleep at night. If you have trouble falling asleep, limit naps or take them earlier in the afternoon.1 Our guide on how to fall asleep faster covers the night-time side.
- Anyone who has to drive soon after waking. Give the grogginess time to wear off first, since it's strongest in the first 30 minutes.4
When to see a doctor
See a doctor if you always feel very tired during the day, or if someone notices that you snore loudly, stop breathing or make gasping, snorting or choking noises while you sleep. These can be signs of sleep apnoea, which can also raise the risk of accidents caused by tiredness, such as car crashes.9
It's also worth getting checked if you start needing long naps every day even though you sleep enough at night, or if you fall asleep during the day without meaning to.
How to take a better nap
- Pick your time: early afternoon, ideally soon after lunch.
- Set an alarm for about 20 minutes, which leaves a few minutes to fall asleep. If you can afford a groggy spell, allow 40–45 minutes for a 30-minute nap.3
- Make it easy to drop off: a dark, quiet spot, or an eye mask and earplugs.
- Try a coffee first if caffeine suits you and it's early in the day.
- Wake up properly: get into bright light or splash your face with water.6
- On training days, treat a nap as part of recovery. The 3-Day Full Body program puts rest days between sessions. After a short night, a short nap before your workout may help, but it doesn't replace a regular bedtime. Follow the program in the TrainSmart app.
A good nap is short, early and occasional. If you find you need one every day, look at your nights first.
