Sleep Calculator

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When do you want to go to bed?
How much sleep do you want?
hours   minutes

This sleep calculator estimates the time you need to go to bed or wake up to get the desired amount of sleep (in terms of number of full cycles of sleep or a specified length of time in hours and minutes). The calculator assumes an average sleep cycle length of 90 minutes, so 5 sleep cycles is equivalent to 450 minutes, or 7.5 hours. Also, take into account the amount of time it takes you to fall asleep, since this is different for different people, and will affect the calculation. To use the calculator, please provide the time you want to wake up or go to bed, select the amount of sleep you want to get, then click the "Calculate" button.

What are sleep cycles?

A sleep cycle is the cycle between non-rapid-eye-movement (NREM) sleep and rapid-eye-movement (REM) sleep. Typically, a person goes through 4-6 sleep cycles per night, which last approximately 90 minutes per cycle, but can range from 70-110 minutes long. Furthermore, an individual's sleep cycle also varies in length throughout the night. For example, an earlier sleep cycle may last 70-100 minutes, while a sleep cycle later in the night may last 90-120 minutes.

Sleep stages:

A sleep cycle is comprised of 4 sleep stages: N1, N2, N3, and REM. The first three stages are the NREM sleep stages and the fourth stage is the REM sleep stage. Normally, a sleep cycle progresses as follows:

  • N1 sleep
  • N2 sleep
  • N3 sleep
  • N2 sleep
  • REM
  • N2 sleep

From the last stage of N2 sleep, the cycle then repeats.

Stage 1 / N1 sleep:

The first stage of sleep, N1, is often referred to as the dozing off stage. This stage can be very short in length, and may last only 1-5 minutes.

In this stage of sleep, the body is not yet fully relaxed, and there are only light changes in brain activity as compared to being awake. Overall, the functions of the body and the brain begin to slow. In this stage, it is fairly easy to wake a person up, thereby interrupting the sleep cycle.

Stage 2 / N2 sleep:

The second sleep stage, N2, is sometimes referred to as the light-sleep stage. This stage typically lasts around 10-25 minutes, and can increase as the night continues. A person typically spends approximately half of their time asleep in N2 sleep over the course of a night.

During this stage of sleep, body temperature starts to decrease, muscles become more relaxed than in the N1 stage, breathing and heart rate slow, and eye movement stops. Brain activity also continues to slow in this stage, but this stage is also characteristic of short bursts of brain activity, referred to as sleep spindles, that have the effect of reducing the chance of a person being woken up. This stage, as well as the following stage, N3, are the stages of sleep during which it is most difficult to wake a person up.

Stage 3 / N3 sleep:

The third stage of sleep, N3, is also referred to as the deep-sleep, slow-wave sleep, or delta sleep stage. Each N3 stage lasts around 20-40 minutes, and people spend more time in this stage of sleep in the earlier parts of the night, but the amount of time spent in N3 decreases as the night goes on, with a shift toward increased periods of REM sleep.

During this stage, muscle tone further decreases along with heart rate and breathing rate, and blood pressure drops. Brain activity also decreases even more than in previous stages of sleep. Also, in this stage of sleep, there is a measurable pattern of slow brain waves (delta waves), hence the names slow-wave and delta-wave sleep.

It is believed that this stage of sleep has many restorative functions that affect a person's growth, immune system, and many other bodily processes. Also, even though brain activity is reduced during this stage of sleep, studies have shown that it affects things such as memory consolidation, creativity, and insightful thinking.

REM sleep:

The fourth stage of sleep is referred to as rapid-eye-movement (REM) sleep. It is the state of sleep during which brain activity most closely resembles activity while awake. It derives its name from the fact that the eyes move rapidly during this stage of sleep. REM sleep can typically only occur after a person has been asleep for around 90 minutes. It can last around 10-60 minutes and the duration of REM sleep tends to increase as the night goes on. On average, it makes up about 25% of sleep, and may only last a few minutes during a person's first sleep cycle of the night.

During this stage of sleep, brain activity increases to levels similar to that of being awake, vivid dreams occur, breathing rate increases and becomes more irregular, rapid eye movement occurs, and temporary paralysis of the muscles occurs (atonia) in part to prevent a person from acting out their dreams. Furthermore, this stage is believed to be an important stage for learning, memory, and creativity, as it is the stage during which information is cemented into a person's memory.

Sleep and health

Sleep has a significant impact on a person's health. Not getting enough sleep can affect both physical and mental health. Lack of sleep impacts higher level reasoning, problem solving, attention to detail, mood, and more. It can also result in an increase in blood pressure leading to adverse events such as heart attack and stroke, obesity, type 2 diabetes, dementia, increased stress, decreased academic performance, and poor mental health.

In addition to getting an adequate number of hours of sleep, it is also important to have a consistent sleep schedule that includes uninterrupted, refreshing sleep. Even if a person gets an adequate number of hours of sleep, if the quality of the sleep is not good, it can still lead to the variety of issues described above. The following table shows the number of hours of quality sleep recommended by the National Sleep Foundation based on age:

AgeRecommended hours of sleep
0-3 months (newborns)14-17
4-11 months (infants)12-15
1-2 years (toddlers)11-14
3-5 years (preschoolers)10-13
6-13 years (school-aged children)9-11
14-17 years (teenagers)8-10
18-25 years (young adults)7-9
26-64 years (adults)7-9
≥ 64 years (older adults)7-8

Factors that affect sleep stages:

There are a number of factors that can affect the sleep stages described in the section above. Some of these include a person's recent sleep patterns, alcohol consumption, and sleep disorders such as sleep apnea, restless leg syndrome, and more.

A person's recent sleep patterns can affect their sleep cycle, particularly if they get insufficient or irregular amounts of sleep over a period of days or more. Examples include those who work night shifts. It can be very difficult to adjust to these types of schedules because they run counter to the body's natural circadian rhythms, which can result in inadequate duration or quality of sleep.

Alcohol consumption also affects sleep in that it decreases the duration of early REM sleep. In later stages of the sleep cycle though, once the alcohol has worn off, the duration of REM sleep may increase to above typical levels to compensate for the decreased duration in early sleep. Often however, this compensation is insufficient.

Sleep disorders such as sleep apnea, restless leg syndrome, and more, can cause interruptions to a person's sleep cycle. This results in a person not completing a proper sleep cycle, or having their sleep cycles frequently interrupted. In such cases, even if a person gets an adequate number of hours of sleep, they may still wake up without feeling refreshed, and may suffer the consequences of sleep deprivation.

Ways to improve sleep:

There are a number of ways for a person to try to improve their sleep. Sleep is complicated and techniques that are helpful for some people may not be helpful for others. In cases where a person practices good sleep hygiene but still wakes up feeling tired or not refreshed, it may be worth checking in with their healthcare provider to examine whether or not the person has any sleep disorders. Below are some tips for increasing the chances of getting good quality sleep.

  • Maintain a consistent sleep schedule
  • Get sufficient natural daylight exposure, at least 30 mins a day
  • Avoid alcohol and large meals before bedtime
  • Eliminate noise and light disruptions during sleeping hours, and keep the temperature cool
  • Exercise daily, but not close to bedtime
  • Avoid nicotine and caffeine
  • Don't take naps after mid-afternoon
  • Limit use of electronics, especially looking at your devices before bed
  • Don't lie in bed awake. If you cannot fall asleep after approximately 20 minutes, get up to do something relaxing
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