Nap Calculator: How Long Should a Power Nap Be?

You're tired, you have half an hour, and you don't want to wake up feeling worse. The calculator above gives you the alarm time, and the guide below explains why short naps usually win and how late is too late.

How long should a power nap be?

A power nap works best at 10 to 20 minutes of sleep. Add the few minutes it takes to drift off, and your alarm goes about 20 to 30 minutes after you lie down. That's long enough to feel rested and short enough to wake from light sleep, so you get up clear instead of foggy.

Here's why. A nap starts in light sleep (stages N1 and N2), and deep sleep (N3) comes after that, as StatPearls' review of sleep stages from the National Library of Medicine describes. The longer you stay down, the likelier the alarm catches you in deep sleep. That's why the Sleep Foundation's napping guide suggests about 20 minutes, and no longer than 30, for most adults.

The best test of nap lengths is small but clear. In a 2006 study in the journal Sleep, Amber Brooks and Leon Lack gave 24 young adults a short night of about 5 hours, then an afternoon nap of 5, 10, 20 or 30 minutes. The 10-minute nap gave the best boost right away, with some benefits lasting up to 155 minutes. The 30-minute nap left people groggy first.

The famous NASA nap points the same way. In NASA's study of planned cockpit rest on long-haul flights, pilots got a 40-minute rest period, slept about 26 minutes on average and stayed more alert through landing.

So when is 90 minutes better? After a really short night, when you have the time and the nap ends well before bed. These are rules of thumb: your own sweet spot may differ a little.

Nap length chart: 10, 20, 30, 60 and 90 minutes compared

Every common nap length on one line: what's likely going on in your brain, how groggy you may feel, what it's good for and when the alarm goes if you lie down at 1:00 PM. The times come from the calculator above, with 10 minutes to fall asleep, so they match it exactly.

A 90-minute nap usually leaves you less foggy than 60 minutes, because a cycle tends to end in lighter sleep. The price is that it's more likely to cut into tonight's sleep.

What is the best time to take a nap?

For most people, the best time to nap is the early afternoon, about 6 to 8 hours after you wake up. If you get up at 7:00 AM, that's 1:00 PM to 3:00 PM. It's when the natural afternoon dip hits, and it leaves plenty of room before bedtime.

The bigger risk is napping too late. The Sleep Foundation's napping guide advises finishing a nap at least 8 hours before bed, which for most people means before 3 PM. The calculator turns that into your own times from your wake-up time and bedtime, and warns you when a nap ends too close to bed.

If you're a natural night owl, your dip may come later than this table suggests. The chronotype quiz shows where your body clock tends to sit.

Napping for shift workers

Working nights? Enter the wake-up time and bedtime of a shift day and the same rules apply: up at 2:00 PM, your window is 8:00 PM to 10:00 PM.

During the shift, keep naps short. In a 2016 simulated night shift study in Sleep, Cassie Hilditch and colleagues found measurable sleep inertia after a 30-minute nap in the middle of the night, and none after a 10-minute nap. When you have to be sharp the moment you wake, 10 to 20 minutes is the safer bet.

How we calculate your nap alarm (and why nap calculators disagree)

The calculator adds three numbers: when you lie down, the time it takes you to fall asleep and the nap itself. It plans with 10 minutes to fall asleep, a 20-minute power nap and a 90-minute full cycle, and you can change each one. Lie down at 1:00 PM and your alarm is 1:30 PM.

1. Start time. Now, from your device's clock, or a time you pick, like 1:00 PM.
2. Plus time to fall asleep. 10 minutes by default, anything from 0 to 30.
3. Plus the nap. 10, 20 or 90 minutes, or your own 5 to 120.
4. Equals your alarm. 1:00 PM + 10 + 20 minutes = 1:30 PM. Past midnight, it says "next day".

Other nap calculators disagree because they guess differently. Some skip the time to fall asleep, others add up to 30 minutes, and the "ideal" power nap ranges from 10 to 30 minutes. We show our numbers so you can adjust them.

"When should I nap?" uses two rules of thumb. Your nap window runs from 6 to 8 hours after you wake up. Your nap should end at least 8 hours before bed, the Sleep Foundation's advice. The latest start time is whichever limit comes first; when the bedtime limit falls before the window opens, that nap is "Not recommended today".

Limits, honestly: the calculator can't see your sleep. How fast you drift off and how long your cycles last vary by person and by day. The labels are good odds, not guarantees.

Why do I feel worse after a nap?

You probably woke up from deep sleep. That heavy, foggy feeling is called sleep inertia. It usually fades once you're up and moving, but it can hang on longer after a long nap or a nap at night. It's the main reason a 60-minute nap can feel worse than a 20-minute one.

A 2019 review of sleep inertia by Cassie Hilditch and Andrew McHill describes it as a temporary drop in alertness right after waking, stronger after deep sleep or at night.

What helps:

• Keep the nap at 10 to 20 minutes.
• Get up at the first alarm. Snoozing buys more of the sleep that makes you groggy, so the timer above has no snooze.
• Find bright light, ideally daylight, right away.
• Move for a minute. Cold water on your face may help too.
• Try a coffee nap next time (below).

One exception: after a short night, your body can drop into deep sleep faster, so even 20 minutes can leave you groggy. That's normal, and a sign to protect tonight's sleep.

Coffee naps: do they actually work?

Yes, for many people. You drink coffee right before a nap of about 20 minutes. Caffeine takes about 30 minutes to kick in, according to the Sleep Foundation's guide to coffee naps, so you're already asleep before it works and it starts helping around the time your alarm goes.

The research behind it comes from the road. In a 1997 driving simulator study, Louise Reyner and Jim Horne found that caffeine plus a nap of under 15 minutes cut sleepy driving incidents more than caffeine alone.

1. Drink your coffee (or another source of caffeine) quickly, at 1:00 PM.
2. Lie down right away. With 10 minutes to fall asleep, you're out by about 1:10 PM.
3. Set your alarm for 1:30 PM: 20 minutes of sleep.
4. Get up when it rings, and let the caffeine do the rest.

When not to: late in the day. A 2023 meta-analysis of 24 studies by Carissa Gardiner and colleagues suggests a cup of coffee (107 mg of caffeine per 250 mL) at least 8.8 hours before bed to avoid losing sleep. The calculator rounds that to 9 hours: with a 7:00 AM wake-up and an 11:00 PM bedtime, start a coffee nap by 2:00 PM. Skip it too if you're pregnant or avoid caffeine for medical reasons.

Is napping good for you? Benefits, risks and when to see a doctor

For most adults, a short nap is good for you: it can lift alertness and performance for up to a couple of hours, as the Brooks and Lack study and NASA's pilot study showed. Napping daily isn't a problem in itself, but needing long naps every day can be a sign worth checking.

The risks are about long, frequent naps, mostly in older adults. In a study of 1,401 older adults in the Rush Memory and Aging Project, Peng Li and colleagues tracked naps with wrist sensors for up to 14 years. Longer and more frequent naps went with a higher risk of Alzheimer's dementia. That's a link, not proof that naps cause harm: more daytime sleepiness may be an early sign instead.

Adults need at least 7 hours of sleep a night, according to the 2015 consensus statement of the American Academy of Sleep Medicine and the Sleep Research Society. If you get that and still need a nap most days, talk to your doctor.

Make your afternoon reset a daily habit

A short nap at the same time every day works better than a random crash on the couch. Tie it to something you already do ("After lunch, I lie down for 20 minutes"), which is habit stacking from our Atomic Habits cheat sheet. Can't sleep at work? Five minutes of breathing, or a pomodoro timer break, is a reset too.

The real fix for a deep afternoon dip is usually the night before. In Greatr you build an evening routine that gets you to bed on time, with habits like breathing, meditation or reading, run one at a time. Every habit earns XP, and your streak grows with each night you show up. The sleep cycle calculator tells you when that bedtime should be.

Your next step: pick tomorrow's nap time from the calculator above, and set the alarm before you lie down.