Last updated on March 15th, 2020
About Our Calculator
Sleepyhood.com’s Sleep Cycle Calculator is intended for informational purposes only. The calculator estimates the best time for adults (age 18-54) to wake up and go to bed. For further reference, we’ve also added sleep time recommendations by the National Sleep Foundation.
What is a Sleep Cycle?
In layman terms, a sleep cycle comprises the various patterns of activity that your brain goes through while you are sleeping. These patterns form a predictable cycle or oscillation. There are two main sleep cycle categories: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. 
How Long is a Sleep Cycle?
The average length of a sleep cycle in an adult is 90 minutes. Both NREM and REM sleep play out in a recurring, push-pull battle for brain domination across the night. The cerebral war between the two is won and lost every ninety minutes, ruled first by NREM sleep, followed by the comeback of REM sleep. 
How Many Cycles of Sleep Do I Need?
Ideally 6 to 5 sleep cycles. Considering that the average length of a sleep cycle is 90 minutes, if you get 8 hours of sleep, you give your body enough time to complete five cycles.
It’s important to keep in mind that not all five cycles are equal. While it is true that we flip-flop back and forth between NREM and REM sleep every ninety minutes, the second half of the night is dominated by REM sleep—cycle 5 is the richest in REM sleep.
What Happens if I Wake Up in the Middle of a Sleep Cycle?
Waking up in the middle of a cycle will throw your body out of alignment and force it to disrupt the natural restorative process of sleep.
Have you ever woken up on the wrong side of the bed or slept for a long time only to feel worse than when you’ve slept less? This is often due to waking up in the middle of a cycle.
Stages of Sleep
Understanding Stages of Sleep
According to the American Association for Sleep Medicine (AASM) classification, there are 5 stages of sleep. As mentioned on our definition of sleep cycles, sleep activity is divided in two categories: NREM and REM sleep. Your brain cycles through all stages of NREM and REM sleep during one sleep cycle every 90 minutes.
REM and NREM Sleep Table
|Type of Sleep||Predominance||Key Function|
|REM Sleep||Later in the night during sleep stages 4 and 5||Strengthening neural connection|
|NREM Sleep||Early in the night during sleep stages 1 to 3||Weeding out and removing unnecessary neural connections|
What are the 5 Stages of Sleep?
- Stage 1: Relaxed Wakefulness
- Stage 2: Light Sleep
- Stage 3: Slow-Wave Sleep (SWS)
- Stage 4: Slow-Wave Sleep (SWS)
- Stage 5: REM Sleep
Stages of Sleep Table
|Stage One||Light sleep. Slow movement and muscle activity. Can easily be interrupted and stopped. Often lasts 10 minutes or less.|
|Stage Two||The longest sleep stage; encompassing 50% of all sleep. Eye movements stop and most brain activity slows to waves.|
|Stage Three||Identified by the presence of delta waves, which signify slower brain activity which is thought to be restorative. Not easily interrupted.|
|Stage Four||Delta waves and little movement in the eyes or throughout the body. Should not be interrupted. Also referred to as deep sleep.|
|Rapid Eye Movement (REM) Sleep||Defined by vivid dreams and lots of movement in the eyes. Thought to be restorative. With each consecutive cycle, this REM stage lasts longer and longer, reducing the amount of time spent in stages three and four.|
How Much Sleep Do I Need?
It’s recommened to prioritize getting complete sleep cycles over getting a certain number of hours of sleep. Doing so will not only give your body the rest it needs to make it through the following day, but also give you a better start in the morning.
After all, insomnia and exhaustion have been found to be more impairing than alcohol or other drugs in some cases.
The amount of sleep you need is heavily based on your age. For example, infants regularly need 16 hours of sleep a day to properly function and grow. Compare that to the recommended amount of sleep for adults—seven to nine hours. The key is to set proper sleeping habits in place and to understand the natural signs your body gives you to come up with the right number for you.
Sleep Time Recommendations
The National Sleep Foundation  released the results of a world-class study that took more than two years of research to complete.
“The NSF has committed to regularly reviewing and providing scientifically rigorous recommendations,” says Max Hirshkowitz, PhD, Chair of the National Sleep Foundation Scientific Advisory Council. “The public can be confident that these recommendations represent the best guidance for sleep duration and health.” The panel revised the recommended sleep ranges for all six children and teen age groups. A summary of the new recommendations includes:
- Newborns (0-3 months): Sleep range narrowed to 14-17 hours each day (previously it was 12-18)
- Infants (4-11 months): Sleep range widened two hours to 12-15 hours (previously it was 14-15)
- Toddlers (1-2 years): Sleep range widened by one hour to 11-14 hours (previously it was 12-14)
- Preschoolers (3-5): Sleep range widened by one hour to 10-13 hours (previously it was 11-13)
- School age children (6-13): Sleep range widened by one hour to 9-11 hours (previously it was 10-11)
- Teenagers (14-17): Sleep range widened by one hour to 8-10 hours (previously it was 8.5-9.5)
- Younger adults (18-25): Sleep range is 7-9 hours (new age category)
- Adults (26-64): Sleep range did not change and remains 7-9 hours
- Older adults (65+): Sleep range is 7-8 hours (new age category)
What Happens If I Skip Sleep?
Skipping sleep, otherwise known as running a sleep debt, is a dangerous and fatiguing practice. Sleep debt is gathered when you deny your body the number of sleep hours and sleep cycles it needs in a night. For example, if you sleep for eight hours under normal conditions but only get five hours one night, you would have a sleep debt of three hours.
Just like with financial debt, sleep debt needs to be repaid. If you are unable to repay the debt, and don’t give your body time to make up for the sleep, signs of sleep deprivation will occur.
While self-diagnosing isn’t always accurate, sleep deprivation can be potentially dangerous and is something to look out for. If you or a loved one is exhibiting many of these signs and often doesn’t get enough sleep, chances are good that a sleep debt is involved.
Sleep debts can be taken care of in multiple ways. While it isn’t always preferable, if you have a day with little or nothing planned coming up on your calendar, consider sleeping without an alarm set to wake you up. Otherwise, you could budget in an extra hour of sleep into your schedule for the remainder of the week or month. Doing so will help you cut back on sleep debt and get back to a regular schedule.
Probably the best way to combat sleep debt is to set healthy sleeping habits in place now so that sleep debt cannot affect you later on.
Tips for Getting a Good Night’s Rest
Sleeping right means taking the time to plan your day around your nights. Provided you’ve taken the time to organize your schedule and have the ability to sleep as many hours as recommended for your age group, the following tips should keep you rested and rejuvenated:
First, remove depressants and stimulants from your evening routine—and possibly from the rest of your day. Energy drinks, coffee, and similar substances can be lifesavers when emergencies strike and you’re forced to skip sleep. While this is perfectly acceptable for the body for one or two nights a month, consistently stimulating your body during the hours before sleep will result in insomnia. A good rule of thumb is to put down the caffeine at least five hours before bed, which matches the half-life of the substance.
Next, you’ll want to play to your body’s natural predisposition to routines. If possible, set up a sleep schedule in which you lay down for bed at the same time each day—even on weekends. A sleep schedule tells your body to prepare for sleep at the right time, every time. You’ll feel tired near bedtime and alert when it’s time to wake up. Much like with stimulants, avoid habitually breaking your schedule to ensure it sticks with your body.
Finally, give your brain the safe space it needs for sleep by ensuring your resting environment is used for resting and that alone. Avoid using or entering your bedroom during the day, and make sure to invest in blackout curtains and cut off all of the lights at night. You also want to make sure the air in your room isn’t too humid or too dry, and that the air remains around 60-68 degrees Fahrenheit.
All of the above aids in ensuring you can sleep well and maximizes the value of the sleep calculator. From cutting out stimulants to laying down the groundwork for rest, there are many tools you can use to optimize your rest to enjoy more energy during the day.
- Matthew Walker, PhD. Why We Sleep. Kindle Edition.