Nap calculator

How the calculator works

It adds the time it takes you to fall asleep to two nap lengths. A short nap is about 20 minutes asleep, which is the length the Sleep Foundation suggests for most adults, with 30 minutes as the upper limit. A full cycle is about 90 minutes asleep.

Say you lie down at 1:30 PM and take 15 minutes to drift off. Set the alarm for 2:05 PM for a short nap, or 3:15 PM for a full cycle.

Why 20 or 90 minutes, and not an hour

The longer you sleep, the more likely you are to reach deep sleep, and being woken from it is what leaves you groggy. The Sleep Foundation says naps longer than 30 minutes can leave you groggy and less sharp afterward. The CDC's guidance for nurses says that waking after about an hour, in deep sleep, can leave you functioning considerably worse for a while.

A nap of about 90 minutes is predicted to end at the close of a sleep cycle, the same CDC page says, so you may wake up less groggy than after an hour. That's why the calculator shows the 30 to 60 minute range as the one to avoid. Waking from deep sleep can leave you foggy for up to 30 minutes or an hour, according to Cleveland Clinic.

Even after a well-timed nap, expect a few minutes of grogginess. The CDC says it may go away within 15 to 30 minutes, and it can last longer if you're very short on sleep.

The best time of day to nap

Most people feel a dip in alertness after lunch, and the Sleep Foundation says just before or during that dip is the best time for a nap. It suggests napping 8 or more hours before bedtime, which for most people means before 3 PM. Enter your bedtime above and the calculator tells you the latest time to start.

Naps and sleep debt

A nap helps you get through the afternoon, but it's not a fix for short nights. If you find yourself needing one most days, the sleep debt calculator shows how far behind your goal you are. Sleep Tiles tracks that every morning from the nights your Apple Watch, Oura Ring, WHOOP or Garmin saves to Apple Health.

Questions

How long should a nap be?

About 20 minutes asleep for most people, and no more than 30, according to the Sleep Foundation. If you have time, a nap of about 90 minutes covers a full sleep cycle.

Why do I feel worse after a nap?

You probably woke up during deep sleep. Naps of 30 to 60 minutes are the most likely to do that. Try a shorter nap, or a full 90 minute cycle.

What is the latest time I should nap?

The Sleep Foundation suggests napping 8 or more hours before bedtime. With a 10:30 PM bedtime, that means starting by 2:30 PM.

Does the calculator count the time it takes to fall asleep?

Yes. Pick how long it usually takes you to drift off, and the alarm times move to match.