Nap calculator
Tell it when you will lie down and how long you usually take to nod off. It gives an alarm time for a quick nap, a short nap and a full-cycle nap, and can run a gentle nap timer for you.
Set your alarm for
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Quick nap
Alarm at 2:20 PM
Short enough to wake up clear-headed; in a sleep lab study, 10 minutes helped straight away.
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Short nap
Alarm at 2:30 PM
Still under 30 minutes, so grogginess is less likely, though the boost may take a little while to arrive.
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Full-cycle nap
Alarm at 3:40 PM
Long enough to pass through deep sleep and come out the other side. Needs a real gap in your day.
- 10–20 min: quick and clear-headed
- 30 min to late in a cycle: more likely to wake groggy
- About 90 min: one full cycle
Not medical advice. If you need naps every day despite a full night in bed, mention it to a doctor.
Nap timer
0:00
Keep this page open with the sound on. Phones may silence background tabs, so use your phone's own alarm for a nap you cannot oversleep.
Which nap to choose
In a sleep-lab study of afternoon naps after a short night, a 10-minute nap improved alertness and performance straight away, with some benefits lasting up to 155 minutes. A 20-minute nap helped too, but the benefit took about half an hour to appear. A 30-minute nap left people groggy at first, and 5 minutes did little (Brooks & Lack, 2006).
That grogginess is called sleep inertia. It is less likely after naps under 30 minutes, possibly because deep sleep usually starts about 30 minutes in, and a review of the evidence suggests keeping naps below that if you need to be sharp soon after (Hilditch & McHill, 2019). A full-cycle nap of about 90 minutes takes you through deep sleep and back out, which is why the ruler shades the middle lengths instead.
Using the timer
The alarm time adds your time to fall asleep to the nap itself. Press Start nap timer on any option to count down on this page with an optional chime. It keeps time from your device's clock, but browsers may pause sound in the background, so rely on a proper alarm when it matters.
Sources
- Brooks A, Lack L. A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? Sleep 2006;29(6):831–840. doi:10.1093/sleep/29.6.831
- Hilditch CJ, McHill AW. Sleep inertia: current insights. Nature and Science of Sleep 2019;11:155–165. doi:10.2147/NSS.S188911
- Cajochen C, Reichert C, Münch M, et al. Ultradian sleep cycles: frequency, duration, and associations with individual and environmental factors. Sleep Health 2024;10(1 Suppl):S52–S62. doi:10.1016/j.sleh.2023.09.002
Questions
Is a power nap really only 10 minutes?
That is minutes asleep, not minutes lying down. If you usually take 10 minutes to nod off, set the alarm for about 20 minutes after you lie down, which is what the calculator does.
Can a nap replace a short night?
No. A nap can help you through the afternoon, but it is not a substitute for regular, sufficient night-time sleep.
Why is the full-cycle option not exactly 90 minutes?
Cycle length varies between people; a large study found a median of 96 minutes. Choose a different cycle length if 90 minutes leaves you groggy.