Nap calculator
Choose how long you want to sleep and when you will lie down. The calculator adds the time it takes you to drift off and tells you when to set the alarm, with what the research says about that nap length.
Quick answer: For a quick lift, nap about 10 minutes. In a lab study of sleep-restricted adults, a 10-minute nap improved alertness straight away for up to 155 minutes. Twenty minutes also helped but took about 35 minutes to kick in, and 30 minutes brought grogginess first. Set the alarm for nap length plus the time you take to fall asleep.
Key facts
- Early afternoon is the most favourable time to nap (Lovato and Lack review)
- Alarm time = when you lie down + time to fall asleep + nap length
- A 90-minute nap is about one full sleep cycle (80 to 100 minutes, NHLBI)
- Naps of 30 minutes or more can bring sleep inertia, a groggy spell, first
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How it’s calculated
Alarm time = the time you lie down + the time you usually take to fall asleep + the nap length you choose (10, 20, 30 or 90 minutes).
- 10, 20 and 30 minutes: the lengths compared by Brooks and Lack, with what each did to alertness[1].
- 90 minutes: roughly one full sleep cycle, which the NHLBI puts at about 80 to 100 minutes[3].
- Late-nap note: if you lie down before 11 AM or at 4 PM or later, it shows a note, because the early afternoon is the most favourable time to nap[2].
Example: lie down at 1:00 PM, 10 minutes to fall asleep, 20-minute nap: set the alarm for 1:30 PM.
How the nap calculator works
The alarm time is simple arithmetic: when you lie down, plus the minutes you usually need to fall asleep, plus the nap itself. The useful part is choosing the length. The four options come from the research below.
What the research found about nap length
In a well-known lab study, Brooks and Lack restricted 24 young adults to about five hours of sleep, then tested naps of 5, 10, 20 and 30 minutes at 3 PM against no nap at all[1]:
- 5 minutes gave few benefits compared with not napping.
- 10 minutes produced improvements straight away that lasted up to 155 minutes. The authors called it the most effective of the lengths tested.
- 20 minutes also helped, but the benefits only appeared about 35 minutes after waking and lasted up to 125 minutes.
- 30 minutes first caused a period of grogginess, known as sleep inertia, before benefits that lasted up to 155 minutes.
A later review by the same group came to a similar view: brief naps of 5 to 15 minutes give benefits almost immediately that last one to three hours, while naps over 30 minutes can bring sleep inertia first and longer-lasting benefits after. It also found the early afternoon to be the most favourable time to nap[2].
The 90-minute option is about one full sleep cycle, which the NHLBI describes as lasting 80 to 100 minutes[3]. It suits a planned long nap, for example before a night shift, more than a quick lift at your desk.
Tips for a nap that doesn’t wreck your night
- Nap early. A short nap in the early afternoon is less likely to push back your bedtime than one in the evening. The calculator warns you when the start time is late.
- Allow for grogginess. After a 30 or 90 minute nap, give yourself time before driving or anything that needs a clear head.
- Mind the coffee. If you want caffeine after your nap, check the caffeine cutoff time for your bedtime first.
- Don’t use naps to cover a big gap. Regular long naps can be a sign you are short on night sleep. The bedtime calculator helps you plan a full night instead.
A steady sound helps some people nap through office or street noise. A fan or white noise is easy to run in the background, and our free sleep sound player has a 15 minute timer.
Questions
What is the best nap length?
In the Brooks and Lack study of sleep-restricted young adults, a 10-minute nap gave the quickest and longest-lasting lift of the lengths tested, with little grogginess. Twenty minutes also helped, but the benefits took longer to appear.
Why do I feel worse after a long nap?
That grogginess is called sleep inertia. Naps longer than about 30 minutes are more likely to cause it, because you may wake from deeper sleep. It usually passes, and benefits can follow.
Should I count the time it takes to fall asleep?
Yes. The nap lengths in the research refer to time asleep, so the calculator adds your usual time to drift off before setting the alarm.
What is the best time of day to nap?
A review of the research found the early afternoon to be the most favourable time. Late naps are more likely to make it harder to fall asleep at night.
Sources
- Brooks A, Lack L. A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? Sleep, 2006.
- Lovato N, Lack L. The effects of napping on cognitive functioning. Progress in Brain Research, 2010.
- National Heart, Lung, and Blood Institute. How Sleep Works: Sleep Phases and Stages. Updated March 24, 2022.
This tool gives general estimates for healthy adults and is not medical advice. If you are often tired despite enough time in bed, snore loudly, or struggle to sleep on most nights, talk to a doctor or a sleep specialist.