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Sleep Calculator

Enter the time you want to wake up. Your bedtime options appear instantly.

Cycle length and time to fall asleep vary by person. Adjust them to fit you.

Everything is calculated in this page. Times are estimates, not a promise of better sleep. If you have trouble sleeping for a long time, talk to a doctor.

How to use

  1. 1. Pick a modeWake-up time, bedtime, sleep now, or nap.
  2. 2. Enter a timeAdjust how long you take to fall asleep and the cycle length to suit you.
  3. 3. Choose an optionTap a time to select it, then copy it or add it to your calendar.

How it works

From a wake-up time, bedtime = wake-up time − time to fall asleep − cycle length × number of cycles. We show 3 to 7 cycles (4 h 30 min to 10 h 30 min with 90-minute cycles).

From a bedtime, wake-up time = bedtime + time to fall asleep + cycle length × number of cycles.

Sources: NIH (NHLBI) Stages of Sleep

How much sleep you need by age (CDC)

Options below your age group’s recommendation are marked “short”, and those above it “long”.

AgeRecommended
18–607 or more hours
61–647–9 hours
65 and older7–8 hours
13–178–10 hours
6–129–12 hours

Sources: CDC – About Sleep

How long a nap should be

The CDC’s NIOSH training for nurses suggests naps of 15 to 30 minutes. Nap mode shows alarm times for 15, 20 and 30 minutes and for one full cycle (90 minutes by default).

Sources: CDC NIOSH – Work hour training for nurses, Module 7

FAQ

Who is this sleep calculator for?

It suits people with a fixed wake-up time who want to know when to go to bed, students planning bedtimes around early classes, people who want to take a short nap at lunch, and parents working out a bedtime for a school-age child.

When is it useful?

For example, at night, to pick a bedtime from tomorrow’s wake-up time. When it is already late, to see wake-up times with Sleep now. At lunch, to set a nap alarm time. Or to add the time you chose to your calendar and get a notification.

What are the benefits of using it?

You don’t have to add and subtract cycle lengths and the time to fall asleep in your head. Options below the recommendation for your age group are marked “short”, so it is harder to pick too little sleep by mistake. Your times and settings stay on this device, so you don’t have to enter them every night.

How many hours of sleep do I need?

The CDC recommends 7 or more hours for adults 18–60, 7–9 hours for ages 61–64, 7–8 hours for 65 and older, 8–10 hours for teens 13–17 and 9–12 hours for children 6–12.

How does the calculator work?

From a wake-up time, bedtime = wake-up time − time to fall asleep − cycle length × number of cycles. From a bedtime, wake-up time = bedtime + time to fall asleep + cycle length × number of cycles. It shows 3 to 7 cycles, which is 4 h 30 min to 10 h 30 min with 90-minute cycles.

Why 90-minute sleep cycles?

The NIH (NHLBI) says a sleep cycle lasts about 80 to 100 minutes and you go through four to six cycles a night. Cycle length differs from person to person, so you can choose 80 to 100 minutes here.

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