Sleep calculator
Pick when you wake up or go to bed, get times that end a sleep cycle.
Your own estimate. NHLBI: a cycle lasts about 80–100 minutes.
How does the sleep calculator work?
Through the night you go through cycles of non-REM 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, and you may wake briefly between cycles. The calculator counts back (or forward) whole cycles of the length you choose — 90 minutes unless you change it — plus the time you usually take to fall asleep.
Example
To wake up at 6:30 AM with 5 cycles of 90 minutes (7½ hours of sleep) and 15 minutes to fall asleep, go to bed at 10:45 PM. With 6 cycles (9 hours), go to bed at 9:15 PM.
How many hours of sleep do I need?
Adults 18 to 60: 7 or more hours a night, per the American Academy of Sleep Medicine and Sleep Research Society. Teens 13 to 18: 8 to 10 hours; children 6 to 12: 9 to 12 hours; ages 3 to 5: 10 to 13 hours, ages 1 to 2: 11 to 14 hours, and infants 4 to 12 months: 12 to 16 hours, naps included, per the AASM pediatric consensus endorsed by the American Academy of Pediatrics. The National Institute of Neurological Disorders and Stroke says most adults need 7 to 9 hours, even older people.
How long does it take to fall asleep?
It differs from person to person and night to night, so the calculator asks for your own estimate. If you often lie awake a long time, that is worth raising with a doctor.
Is a sleep cycle always 90 minutes?
No — about 80 to 100 minutes, per NHLBI, and it varies through the night: the National Institute of Neurological Disorders and Stroke notes that REM periods get longer toward morning. Treat the times as a guide and adjust the cycle length if you know yours.
Should I count from lights-out or from falling asleep?
From the moment you actually fall asleep. That is why the calculator adds your fall-asleep time to the cycles: five 90-minute cycles plus 15 minutes of lying awake puts bedtime at 10:45 PM for a 6:30 AM alarm, not 11:00 PM.
Do naps follow the same cycle math?
The cycle idea describes a night of sleep, and the calculator is built for that. A short nap does not have to fit whole cycles, so the bedtime figures on this page are not meant for planning one.
How the times are worked out
Each answer is a simple subtraction: wake-up time minus the time you take to fall asleep, minus a whole number of cycles of the length you chose. In "wake up at" mode the table lists bedtimes for 7, 6, 5, 4 and 3 cycles; in "go to bed at" mode it adds the same amounts to your bedtime to give wake-up times. The calculator highlights the smallest number of whole cycles that still meets the recommended amount for the age group you pick, because a time that appears in the table is not automatically enough sleep. The result is arithmetic on a typical pattern, not a measurement of your own sleep stages.
Worked example: waking at 6:30 AM
Take a 90-minute cycle and 15 minutes to fall asleep. Six cycles are 9 hours of sleep, so go to bed at 9:15 PM. Five cycles are 7.5 hours, bedtime 10:45 PM. Four cycles are 6 hours, bedtime 12:15 AM. In the other direction, lying down at 11:00 PM and needing 20 minutes to fall asleep, five cycles end at 6:50 AM.
Why the cycle length matters
The cycle is not fixed at 90 minutes; the National Heart, Lung, and Blood Institute gives a range of 80 to 100. Over five cycles that range is a spread of 100 minutes. With the same 6:30 AM alarm and 15 minutes to fall asleep, five 80-minute cycles mean bed at 11:35 PM, and five 100-minute cycles mean bed at 9:55 PM. If you consistently wake up groggy at the suggested times, changing the cycle length in the form is a more useful experiment than trusting the default.
Common mistakes
Treating the first time in the table as the target: it is a menu, and the amount of sleep in the left-hand column should still fall in the recommended range for your age. Entering zero minutes to fall asleep when you usually lie awake for a while makes every bedtime too late. Using the table for an irregular schedule is another trap; the cycle math says nothing about being awake at the wrong time of day. If you often sleep far less than you planned, or you are tired despite long nights, that is a question for a doctor rather than a different alarm time.
Sources: National Heart, Lung, and Blood Institute, sleep phases and stages (cycles of 80 to 100 minutes); National Institute of Neurological Disorders and Stroke, brain basics on sleep; American Academy of Sleep Medicine and Sleep Research Society consensus on recommended sleep durations. Related: time calculator, age calculator and water intake calculator.
For general information only — not medical advice. Talk with your doctor or another health professional about your own health. How we check our calculators.