Free tool · Sleep

Nap calculator

Short answer

In a sleep lab study of afternoon naps after a short night, a 10-minute nap improved alertness and performance straight away, for up to 155 minutes. A 20-minute nap's benefits arrived about 35 minutes later, and a 30-minute nap left people groggy first. Lying down at 2:00 PM and falling asleep in 5 minutes, set the alarm for 2:15 PM for a 10-minute nap.

Last reviewed 27 October 20262 published sourcesNot medical advice

Reps keeps track of this for you on iPhone, iPad and Apple Watch.

Get Reps free

Nap calculator

Set your alarm for the nap length you want, counted from when you fall asleep.

h

24-hour clock: 13 is 1 PM.

min
min

Leave blank for 5 minutes.

Enter when you will lie down.

Runs entirely in your browser. Nothing you type is saved or sent anywhere.

Alarm times if you lie down at 2:00 PM and fall asleep in 5 minutes
NapAlarmWhat to expect
10-minute nap2:15 PMBrooks & Lack's best short nap: alert straight after
20-minute nap2:25 PMBenefits arrive about half an hour after waking
30-minute nap2:35 PMExpect some grogginess first
90-minute nap3:35 PMAbout one full sleep cycle; not tested in the study
Nap lengths are minutes of sleep, counted from falling asleep. 4 lengths shown.

What the nap study found

Twenty-four healthy young adults slept about 5 hours at home, then took a 3 PM nap of exactly 5, 10, 20 or 30 minutes of sleep, or no nap. The 5-minute nap did little. The 10-minute nap improved sleepiness, fatigue, vigour and cognitive performance at once, some for up to 155 minutes; the 20-minute nap's gains emerged 35 minutes after and lasted up to 125 minutes; the 30-minute nap brought sleep inertia first (Brooks & Lack, 2006).

REM sleep first appears about 90 minutes after falling asleep (NINDS), which is why a 90-minute nap is treated as one full cycle; real cycles vary between people. Plan tonight's bedtime with the sleep calculator, and keep afternoon coffee from undoing it with the caffeine calculator.

Naps, nights and your energy

Reps reads your Apple Watch sleep and shows how last night and today's naps feed your energy through the day.

Download Reps on the App StoreSleep and energy in Reps

Free to download · iPhone, iPad and Apple Watch

Common questions

What is the best nap length?

Of the lengths tested in Brooks and Lack's study (5, 10, 20 and 30 minutes of sleep), 10 minutes worked best overall: benefits came at once and lasted up to 155 minutes. Five minutes did little.

Why do I feel groggy after a nap?

That is sleep inertia. In the same study, a 30-minute nap brought a spell of lower alertness and performance right after waking, before its benefits arrived. Short naps avoid most of it.

Is a 90-minute nap better?

It is a different kind of nap. A 90-minute nap is treated as about one full sleep cycle, while the study above tested naps of up to 30 minutes. For a quick boost in the afternoon, the short naps are the ones with evidence behind them.

Sources

Figures on this page were checked against these publications on 27 October 2026.

  1. 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.org/10.1093/sleep/29.6.831
  2. National Institute of Neurological Disorders and Stroke. Brain Basics: Understanding Sleep (last reviewed 25 February 2025). www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep

More sleep and caffeine tools

See every free tool →