Tools Sleep Calculator

Free tool · Sleep Calculator

When should I go to bed, and how much sleep am I missing?

Sleep runs in cycles of roughly 90 minutes. Pick the time you need to wake up (or the time you’re going to bed) to get bedtimes that fit whole cycles, then add the hours you slept this past week to see your sleep debt against the recommended amount for your age.

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Step 1 · Your bedtime

What do you want to work out?
We’ll count back in 90-minute cycles.
15 is a common default. Use what’s typical for you.

Step 2 · Your age

Recommended sleep per 24 hours, from the CDC.

Step 3 · Your past week (optional)

How do you want to enter your sleep?
Hours actually asleep, not time in bed. 6.5 means 6 hours 30 minutes. Leave a night blank if you don’t remember it.

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Beyond sleep

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How this calculator works

Bedtimes. Through the night you move through cycles of lighter non-REM sleep, deep sleep and REM sleep. The National Heart, Lung, and Blood Institute says a cycle starts over every 80 to 100 minutes, usually four to six times a night, so the calculator uses 90 minutes and adds the time it takes you to fall asleep.

Bedtime = wake-up time − (cycles × 90 minutes) − minutes to fall asleep

It suggests five or six cycles, which is 7.5 or 9 hours of sleep, and flags any option below the recommended hours for your age. Four cycles (6 hours) is shown for short nights but falls under the 7-hour minimum for adults.

Sleep debt. The recommended amounts come from the CDC’s table, which is based on consensus statements from the American Academy of Sleep Medicine and the Sleep Research Society. For each night, the calculator counts how far you fell short of the minimum for your age, then adds up the week.

Sleep debt = sum of (recommended hours − hours slept) on each short night

A night with more than enough sleep counts as zero, not as credit. The bands are measured in nights: under an hour is well rested, less than one full recommended night is a little short, one to two nights is sleep debt, and more is deep sleep debt. For habits that help, read our guide on how to sleep better.

Words you’ll see

Sleep cycle
One pass through the stages of non-REM sleep and then REM sleep. Most people go through four to six a night.
REM sleep
Rapid eye movement sleep, the stage when most vivid dreaming happens. The first REM period comes about 90 minutes after you fall asleep, and REM periods get longer toward morning.
Time to fall asleep
The minutes between lying down to sleep and actually falling asleep. Doctors call it sleep latency.
Sleep debt
The hours of sleep you missed compared with what is recommended for your age, added up over several nights.

Common questions

What time should I go to bed if I wake up at 6 a.m.?

Allowing 15 minutes to fall asleep, aim for 8:45 PM for six 90-minute cycles (9 hours of sleep) or 10:15 PM for five cycles (7.5 hours). Both give an adult at least the recommended 7 hours. If you usually take longer to fall asleep, go to bed that much earlier.

How long is a sleep cycle?

The National Heart, Lung, and Blood Institute says the cycle of non-REM and REM sleep starts over every 80 to 100 minutes, with four to six cycles a night. The National Institute of Neurological Disorders and Stroke notes that REM sleep first comes about 90 minutes after you fall asleep. That is why sleep calculators use 90 minutes, but your own cycles can run shorter or longer.

How much sleep do I need?

The American Academy of Sleep Medicine and the Sleep Research Society recommend that adults sleep 7 or more hours a night on a regular basis. The CDC lists 7 or more hours for ages 18 to 60, 7 to 9 hours for 61 to 64, and 7 to 8 hours for 65 and older. Teens 13 to 17 need 8 to 10 hours, and children 6 to 12 need 9 to 12 hours.

How do you calculate sleep debt?

For each night, subtract the hours you slept from the recommended amount for your age, counting zero when you slept enough, then add up the week. An adult who sleeps 6 hours on five weeknights and 8 hours on the weekend has 5 hours of sleep debt. This calculator does not let a long night cancel a short one.

Is it better to wake up at the end of a sleep cycle?

Sleep calculators time your alarm to the end of a cycle on the idea that waking from lighter sleep feels easier than waking from deep sleep. Real cycles vary from about 80 to 100 minutes, so treat the times as a starting point. Getting enough total sleep on a regular schedule matters more than hitting an exact minute.

Sources

  1. How Much Sleep Do I Need? (About Sleep), Centers for Disease Control and Prevention
  2. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society (Watson et al., 2015), Journal of Clinical Sleep Medicine
  3. Recommended Amount of Sleep for Pediatric Populations: A Consensus Statement of the American Academy of Sleep Medicine (Paruthi et al., 2016), Journal of Clinical Sleep Medicine
  4. How Sleep Works: Sleep Phases and Stages, National Heart, Lung, and Blood Institute
  5. Brain Basics: Understanding Sleep, National Institute of Neurological Disorders and Stroke

This tool is for informational and educational purposes only. It is not medical advice and does not diagnose sleep problems. If you are often tired despite enough time in bed, or you snore loudly or stop breathing in your sleep, talk to a doctor.