Nap Calculator: When to Set Your Nap Alarm
Tell it when you lie down and how long you usually take to drift off. It gives the alarm time for a quick power nap, a 20 minute nap, or one full sleep cycle, based on sleep research.
Power nap, 10 min asleep
Fastest boost in the 2006 study below, with gains lasting up to about 2.5 hours.
Short nap, 20 min asleep
Ends before deep sleep, so grogginess is smaller and clears faster.
Full cycle, 90 min asleep
About one sleep cycle. For a big sleep debt or before a night shift.
In Alarm Clock Planner, press and hold the + button for a 10, 15, 20 or 30 minute nap in one tap, or a nap that ends at the top of the next hour. It rings even with the Silent switch on.
How the calculator works
It adds two numbers to the time you lie down: how long you usually need to fall asleep, and how long you want to be asleep. Nap research counts minutes of actual sleep, not minutes in bed, so the time you take to drift off matters. If you are not sure, 10 minutes is a reasonable starting guess; adjust it after a few naps.
Why 10 to 20 minutes works best
A 2006 study in the journal Sleep compared naps of 5, 10, 20 and 30 minutes taken at 3 PM after a short night. The 10 minute nap improved alertness and performance right away, with some gains lasting up to 155 minutes. The 20 minute nap helped too, but its gains appeared about 35 minutes after waking. The 30 minute nap left people groggy at first. A later review by the same group found the same pattern across the research: naps of 5 to 15 minutes help almost immediately for 1 to 3 hours. NIOSH, the US workplace safety institute, advises a brief nap of under 20 minutes for people on a daytime schedule.
Why not an hour
NIOSH explains that sleep gets deeper the longer you sleep and reaches its deepest stage, slow wave sleep, in about an hour. Waking from deep sleep brings sleep inertia: a temporary drop in performance and mood that usually lasts 30 to 60 minutes. Waking at about 20 minutes, before deep sleep, or at about 90 minutes, the predicted end of a sleep cycle, makes it more likely that you wake from light sleep and that the fog clears within 15 to 30 minutes.
Very short of sleep? NIOSH notes that your brain may reach deep sleep sooner, so even a short nap can leave you groggy for longer. Give yourself extra time before driving or anything that needs a clear head.
When a 90 minute nap makes sense
The longer you have been awake, the more a longer nap pays off compared with a short one, according to the review by Lovato and Lack. A full cycle suits the afternoon before a night shift or a day after very little sleep. On a normal day, a short nap is the better trade.
The best time of day to nap
The same review names the early afternoon as the most favourable time for a nap, when alertness naturally dips. For more on choosing a nap length and setting it up on iPhone, see how to set a quick nap alarm on iPhone.
Frequently asked questions
How long should a power nap be?
About 10 to 20 minutes of sleep. In a 2006 lab study of 5, 10, 20 and 30 minute naps after a short night, the 10 minute nap gave the fastest and broadest boost. NIOSH advises a brief nap of under 20 minutes for people on a daytime schedule, with an alarm set 15 to 30 minutes out.
Is a 90 minute nap better than a 60 minute one?
Usually, yes, for how you feel on waking. NIOSH notes that sleep reaches its deepest stage in about an hour, and waking from it can leave you groggy. Around 90 minutes is predicted to be the end of a sleep cycle, so you are more likely to wake from light sleep.
Why do I feel worse after a nap?
That fog is called sleep inertia. NIOSH describes it as a temporary drop in performance and mood after waking that usually lasts 30 to 60 minutes. It is strongest when you wake from deep sleep, which is why a short nap or a full cycle works better than an hour.
Why does the calculator ask how long I take to fall asleep?
The nap lengths in the research count minutes of actual sleep, not minutes lying down. If you need 10 minutes to drift off, a 10 minute nap needs an alarm 20 minutes after you lie down.
Sources
- Brooks and Lack, A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? Sleep, 2006
- Lovato and Lack, The effects of napping on cognitive functioning. Progress in Brain Research, 2010
- NIOSH training for nurses, Module 7: Nap duration
- NIOSH training for nurses, Module 7: Sleep inertia
Set the nap alarm in one tap
Alarm Clock Planner is free on the App Store for iPhone. Hold + for a 10, 15, 20 or 30 minute nap.
