Sleep Calculator

1. Using the sleep calculator
2. How many hours of sleep do I need?
• Typical total sleep time by age
3. Why sleep cycles are important
• Best sleep phase to wake up
4. REM sleep
• How much REM sleep do you need?
5. Factors affecting duration and quality
• How to get a better sleep
6. Health risks associated with poor sleep

    Using the sleep calculator

This tool can be used as a bedtime calculator or wake up time calculator. In both cases, it uses the total sleep time recommended for a given age and an appropriate sleep cycle duration to suggest a bedtime or wake up time that would leave a typical person of that age well-rested and refreshed. The calculator aligns the sleep needed with full cycles for a better wake up experience.

1. Specify the time you expect to get into bed (bedtime), or the desired wake up time (for example, the time you would set your alarm to).
2. Select your age range. This automatically adjusts the cycle duration, but also lets our sleep calculator by age estimate how much sleep is recommended for well-being and best health outcomes.
3. Adjust the "time to fall asleep" based on how long it takes you, on average, to wind down before falling asleep.
4. Optionally, enter a custom cycle duration if you are certain that your sleep cycles are shorter or longer than average *

* Please, note that most wearable devices' sleep stage assessments are inconsistent when compared to accurate measurements taken with polysomnography (PSG) ^[1].

The sleep cycle calculator will output a recommended bedtime or wake up time depending on the task, as well as a shorter sleep scenario. For both scenarios it prints how long you will spend in bed in hours and minutes as well as how many full sleep cycles you will do. Finally, it also shows the estimated REM sleep time based on population statistics, so it doubles as a REM sleep calculator.

    How many hours of sleep do I need?

While it is difficult to answer this question definitively for each and every person, there are a large number of studies on the typical amount of sleep recommended for different groups of people. The most authoritative of these is the "National Sleep Foundation’s updated sleep duration recommendations: final report" ^[2] which outlines the recommended, appropriate, and not recommended durations calculated for all age groups.

The table below is based on the report's findings and recommendations as it contains the most up-to-date consensus recommendation for how much a person should sleep based on their age, assuming there are no health conditions that might necessitate otherwise. The recommended times are in line with other consensus statements ^[3] and can be interpreted as sleep requirements by age.

How many hours of sleep needed by age

Age group (range)	Recommended sleep time*	Appropriate sleep time*
Newborn (0-3 months)	14-17 hours (including naps)	11-19 hours (including naps)
Infant (4-12 months)	12-15 hours (including naps)	10-18 hours (including naps)
Toddler (1-2 years)	11-14 hours (including naps)	11-14 hours (including naps)
Preschool (3-5 years)	10-13 hours (including a nap)	8-14 hours (including a nap)
School-age (6-13 years)	9-11 hours	7-12 hours
Teen (14-17 years)	8-10 hours	7-11 hours
Young Adult (18-25)	7-9 hours	6-11 hours
Adult (26-64)	7-9 hours	6-10 hours
Older Adult (65 and above)	7-8 hours	6-9 hours

* the times are on a daily basis, and include naps where indicated

As the report notes: "Sleep, like diet and exercise, strongly influences many aspects of health including physical, cognitive, and emotional health. Although most individuals' sleep duration falls within the "recommended" range, individuals and their physicians should carefully consider cognitive, physical, and emotional health when sleep durations do not". Our sleep calculator uses the above guidelines when calculating how many hours to recommend for any specified age group. More on night sleep quality, quantity, and their effects on well-being below. Also see how much sleep do you need for more on what quantity is required by age.

Typical total sleep time by age

The graph below is based on a reconstruction of the comprehensive meta-analytical data in Ohayon M.M. et al. 2004 ^[5] and includes data on the sleep hours of 2009 people, mostly measured by polysomnography.

Each rhombus is the mean time of a separate study subgroup. Individual sleep hours are more varied than the averages of even small populations. The best regression fit is achieved by a power curve with R² = 0.60 meaning that if the model is adequate, changes in age explain 60% percent of the variance in total sleep time.

    Why sleep cycles are important

If you had a chance to observe someone sleeping you would know that sleep isn't uniform throughout the night. An adult typically goes through several sleep cycles lasting about 90 minutes on average. Each cycle consists of four different phases: lightest sleep (N1), followed by light sleep (N2), deep sleep (N3), and finally Rapid-Eye-Movement sleep (REM). Not all cycles are the same length and with each cycle one spends less time in the deep phase and more time in the REM and light phases.

Best sleep phase to wake up

We've all been awakened by an alarm, security siren, our dog, cat, or kid, only to feel groggy and tired for at least the first hour or two of our day. The key to avoiding this is to wake up in stage one (N1) or two (N2), both of which are light sleep phases. Waking up during stage three is likely to feel the worst and our sleep cycle calculator aims to help you avoid that.

In particular, the calculator calculates your total sleep time such that you have higher probability of waking up at the end of a cycle or in the early stages of the next one. This ensure you will feel energized and ready to start your morning routine, given you also got your recommended sleep time.

    REM sleep

In REM sleep the eyes move rapidly while the lids remain closed. In this condition the breath rate increases and the body is temporarily paralyzed. It is in this state that we dream and while it happens our brain waves look similar to those that would be observed during wakefulness.

How much REM sleep do you need?

The amount of REM sleep needed shifts with increasing age. While newborns spend about half their total sleeping time in REM, this percentage starts to decrease by 6 months old and continues to decline throughout childhood ^[4]. By age 5 it is already in the 23-24% range, on average ^[5]. Adults over 18 years of age typically spend about 20% of their total sleep time in the REM phase. This changes little if at all even in older adults, with some studies suggesting a slight dip in REM sleep percentage in the mid-70s ^[5][6][7].

What is interesting is that people tend to spend more time in REM sleep at later cycles, hence it is important to get uninterrupted sleep. It is also why interruptions early in the night have the worst effect on the amount of REM sleep one gets.

    Factors affecting duration and quality

Age is a primary factor related to how much sleep hours one needs. Multiple meta-analyses point to an average decrease of 8-10 minutes per decade in average sleep time, with the decrease being up to 25% more pronounced in women as compared to men ^[6][8]. One study specifically examines the sharp drop in the hours of sleep between ages 11 and 15, especially pronounced during school days as opposed to weekends.^[9]. Another one suggests that the effect of age may be moderated by BMI, drawing yet another link between body weight and health outcomes ^[10].

Sleep efficiency (percentage of sleep time from total time in bed) also slightly decreases with age as older people tend to wake up more often during the night ^[8]. The older you are, the higher percentage of your sleep is spent in light sleep at the detriment of deep sleep.

How to get a better sleep

One cannot do anything about their age or their sleep cycle length (90 min or otherwise). However, the sleeping environment, bedtime routine, and overall sleep habits can be key in securing a long uninterrupted sleep time. Consider these ways to improve your sleep quality:

• Keep to a consistent sleep schedule (bedtime and wake up time)
• Reduce or eliminate noise and light disruptions.
• Get natural daylight exposure.
• No alcohol before bedtime.
• Use an air conditioner to keep the bedroom cool. The ideal temperature is 72-75°F (22-24°C).
• Invest in a comfortable mattress, pillow, and bedsheets
• Avoid mental stimulation, especially intense TV shows or computer games, shortly before bedtime.
• Consider melatonin treatment, shown to have a modest effect^[11]

Our sleep calculator in particular may be useful in keeping your schedule consistent and your sleep hours in line.

    Health risks associated with poor sleep

Sleep is essential for optimal health in children and adolescents, but has also been shown to be beneficial in adult populations. It helps with energy regeneration, self-repair and recovery, as well as brain maintenance. Having a good enough sleep duration and quality is therefore important for physical health, neurocognition, emotion and behavior. The strongest effects are registered in the emotional dimension in school-age children and teenagers (6–18 years old). Compared to the baseline population (adults 18 and above), the 6-18 years group showed a greater propensity for serious adverse effects when they suffered from sleep deficiencies ^[12].

Unfortunately, students often sacrifice sleep due to academic demands, electronic device usage, or lack of awareness about the importance of adequate sleep. Therefore, the persons most likely to be negatively affected by lack of sufficient sleep or poor quality one are also often those who do not take sufficient measures to ensure better night time.

The health risks which increase with a decrease in sleep quality and quantity are:^[12]

1. Emotional and behavioral, which include smoking behavior, non-suicidal self-harm in adolescents, and hyperactivity / inattention, emotional symptoms, conduct problems, and peer relationship problems in children;
2. Neurocognitive such as cognitive and language development, fine and gross motor abilities, and receptive vocabulary in children, and cognitive decline in adults;
3. Physical health outcomes, including new-onset asthma, obesity, problems with maintaining balance, cardiovascular events, all-cause mortality, and risk of hypertension (high blood pressure). In children these include specific serum cytokines;

The general negative expressions of poor sleep include tiredness during the day, slower thinking, slow reaction times leading to errors and accidents, reduced focus and memory, irritability. Feelings of anxiety or depression may appear or get accentuated. Health issues may also include immune function, type 2 diabetes, and kidney disease.

Ensuring one gets enough sleep by following the recommended hours for their age is a good way to reduce the above risks. Our sleep time calculator can help set a bedtime and/or wake up time that facilitates that. Understanding how much sleep one will get with a given bedtime or did get with a given bedtime and wake up time may be a good first step towards improving their sleep habits. A simple hours between calculator can also help with this.