Sleep Calculator

This sleep calculator will help you find the best bedtime for you, by maximizing your full sleep cycles. Sleep consists of 90-minutes-long sequences, repeated throughout the night. You’ll wake up feeling better if you wake up at the end of a cycle, rather than in the middle of it, so use this calculator to find out what time you should go to sleep if you want to wake up refreshed and alert. And if you are still wondering how important it is to get the right amount of sleep, check how deadly your current sleeping routine is!

If you’re interested in how much sleep we need at different ages, whether 6 hours of sleep is enough, what our natural sleep pattern is and what are good sleep habits – keep scrolling and you’ll find the answer.

What are sleep cycles and stages of sleep?

While sleeping, our brains go through several sleep cycles. An average person needs 5-6 cycles to feel fully regenerated in the morning. One sleep cycle lasts around 90 minutes and consists of 5 stages: the first four stages are non-REM stages, where stage 1 and 2 are known as light sleep stages, stage 3 (and 4 in the previous definition) are deep sleep stages, and the last one is REM (rapid eye movement) sleep.image with definition of sleep cycle

The duration of each stage oscillates between 5 and 15 minutes. Early in the night, stages of deep sleep are longer than REM sleep, but this swaps round as the night progresses. People’s brains usually don’t go from stages 1 to 5, but rather: stages of light sleep, stages of deep sleep, REM, and then back to stages of light sleep and stages of deep sleep.

Hypnogram - one sleep cycle

Light sleep stages (N1, N2) are characterized by muscle contractions and being woke easily. Your body is preparing, slowly, for deep sleep, with your brain waves becoming slower.

Deep sleep stages (N3, previously divided into N3 and N4) are also known as delta sleep or slow wave sleep. It’s very hard to wake someone during this stage. It’s also the most important sleep stage as it refreshes you the most and reduces your need for sleep. That’s why if you nap for too long during the day (entering deep sleep) you don’t feel as sleepy that night. Also, during this stage, your body and muscles are being restored by growth hormones.

REM sleep stage (R) is where dreams happen. Your brain imitates waves just as if you were awake, with your eyes moving rapidly but still closed.

image with definition of sleep stages

How long is a sleep cycle?

As we mentioned before, the average sleep cycle is 90 minutes. However, different sources give the values, varying between 90–110 minutes or even 80–120 minutes. Also, sleep cycles increase with age, starting from only 50-60 minutes during infancy.

Animals have similar sleep patterns: a rat’s cycle is as short as 12 minutes, a cat’s – 30 minutes and an elephant’s cycle is ~120 minutes. On average, it’s proportional to the size and the metabolism rate of the animal – the smaller it is, the shorter sleep cycles it has.

Why is a good night’s sleep so important?

While sleeping, our bodies are regenerating, which is why the quality of your sleep is very important. Waking up at the end of a sleep cycle makes you feel refreshed and happier; your body is ready to face the day! The benefits of a good night’s sleep are also: better skin, no dark circles under eyes, smaller chances of eating disorders, a healthier life routine, and a great mood!

Sleep deprivation

Who isn’t guilty of going to sleep too late because of ‘binge-scrolling’ FB or Twitter? Its not just a social media addiction that means we sleep late; we often eat late, drink alcohol or just stare at the TV without realizing it all leads to sleep deprivation that can cause, amongst other things, insomnia, premature skin aging, decreased sex drive, and concentration problems.

It is said that stress and irregular sleeping patterns can also lead to more nightmares, as well as weight gain. Not to mention being grumpy, miserable and easily irritable – things that can seriously affect your relationships with other people. Recently, it has been proven that sleep deprivation puts you also at higher risk of premature mortality! For more information see the sleep deprivation and premature mortality risk paragraph.

How to improve your sleeping habits?

A person who sleeps for only 4 full cycles (90 minutes each) feels better after waking up than someone who slept for 7 hours because they woke up at the end of their last cycle.

  1. Set up alarmsYes, alarms. Setting an alarm for both the time you should go to sleep and wake up can help in getting into a new, healthier routine. Plus, it’s a friendly reminder for people who tend to ‘get lost’ on the Internet. Endless meme scrolling is fun, but it’ll affect your day.
  2. Stop using the snooze buttonAlthough getting ‘just 5 minutes more’ may feel great at first, in the long run snoozing results in you feeling more tired in the morning, because these 5 or 10 minutes are not enough for your body to fall into the precious deep sleep. Believe us, it’s worth getting up with your first alarm, however hard that may be.
  3. No phone or computer policyIt’s also worth it to stop playing with your phone or computer at least 2 hrs before bedtime, as the blue light that their screens emit affects your levels of melatonin (a sleep-inducing hormone), and, as a result, falling asleep takes longer. Say goodbye to FB, TV, and your tablet and enjoy a good night’s sleep!
  4. No alcohol or coffee before sleepWe all know that falling asleep after drinking is faster than if you were sober, but is it healthy? Bad news here – it decreases the quality of your sleep, and in fact it causes you to sleep less than you should to fully regenerate. Caffeine from coffee or theine from tea can also make falling asleep more difficult, so, before you go to bed choose the infusions with chamomile or valerian.
  5. Napping is great!Remember in kindergarten when you hated your afternoon nap? As soon as you start staying up late, you realize how much you miss these obligatory naps. If you ever feel exhausted during the day, try to include a healthy 15-20 min nap in your routine. It is proven to be way more refreshing than a full 90-min sleep cycle in the middle of the day.
  6. Regularity is keyOne way of improving your sleep quality is keeping going-to-bed and waking-up times regular. Every day, you should try to respect your sleep patterns – indulgence once in a while shouldn’t be a problem (like sleeping in until noon on a Sunday), but don’t make a habit out of it.
  7. Have a look at your bed and bedroomTL;DR – think of your bedroom as a cave – it should be cool, dark and quiet. And comfy as well.”You’ve made your bed, now lie on it”. Take a critical look at a few essential aspects which can affect the quality of your sleep:
  • Temperature in the room.Your bedroom should be cool – it should typically range between 60-67 °F (which is 15-19 °C – check it out with our temperature converter) or 65 – 72°F (18-22 °C). However, recommending specific values is difficult, as the comfortable temperature for one person may be not appropriate for another – so if it’s too cold and you can’t sleep, increase the temperature and adjust it to your needs. Just remember that it’s easier to fall asleep in a cooler room. Also, too high a temperature affects the REM sleep stage, essential for normal body physiology, so make sure that the heat doesn’t affect your rest time.
  • As dark as possible.Darkness is essential to having a good quantity and quality of sleep. Light alters our internal sleep clock by inhibiting the rise of melatonin, a sleep hormone. Make sure to remove all unnecessary sources of light – install curtains and shades in windows to block out light (blackout curtains are the best ones) and consider using a sleep mask if you’re traveling or sleeping in a place where it’s difficult to block out light (e.g. summer camping above the Arctic Circle). Preparation for bedtime is also an important issue – the intensity of light measured in lux shouldn’t exceed 180 lux (an average home is around 300-500 lux) for at least an hour before going to bed. Your body needs this time to quiet down, relax and prepare for sleep, so we’ll remind you once again – don’t stimulate your brain with any artificial lights from screens.You can read more about how light affects our sleep here.
  • Noise free area.That’s the third significant feature for a sleep-friendly bedroom – good acoustic climate for sleep. According to WHO guidelines, the average night exposure should not exceed 40 decibels (dB), which is the approximate level of a quiet street. This study showed that room acoustics are important and it can influence our sleep patterns, deep sleep and REM sleep. Sleep phases are shortened in bedrooms that are not acoustically insulated.
    How can you deal with noise disturbing your nights rest? You can start from trying to modify your bedroom: by rearranging or adding some extra pieces of furniture to muffle the sound, investing in floor and ceiling insulation if noisy neighbors are the problem, sound-proofing your windows or covering the walls with absorbent acoustic panels. If these solutions are not possible or they don’t give expected results, you can use active masking (white noise from fan or music) or earplugs (snoring partners can be a nuisance).

Another obvious thing affecting your sleep is your bed itself. A comfy mattress and a supportive pillow are also important for good sleep hygiene.

How much sleep do I need?

It all depends on the person and their age, as some of us feel great after only 6 hrs of sleep every night. However, according to the National Sleep Foundation, we need more than that:

  • Newborn to 3 months old: 14 – 17 hrs
  • 4 to 11 months old: 12 – 15 hrs
  • 1 to 2 years old: 11 – 14 hrs
  • 3 to 5 years old: 10 – 13 hrs
  • 6 to 13 years old: 9 – 11 hrs
  • 14 to 17 years old: 8 – 10 hrs
  • Young adults (18 to 25 years old): 7 – 9 hrs
  • Adults (26 to 64 years old): 7 – 9 hrs
  • Older adults (65+): 7 – 8 hrs

Is 6 hours of sleep enough?

Well – as usual – it depends. The values above are the recommended durations by National Sleep Foundation, but they are averaged over the entire population – everybody is different and other sleep times may be appropriate. Some people only need sleep for 4 or 5 hours – Margaret Thatcher was one of these short-sleepers, as she claimed to sleep only four hours a night. On the other hand, some people (long-sleepers) are drowsy if they don’t sleep for 11 or 12 hours. Why is it so?

The response is simple – how much sleep you need is genetic, like your height or eye color. In 2009, scientists found the gene (DEC2) associated with the “effectiveness” of sleep. Other researchers in 2014 compared how twins performed on some cognitive tasks – one sibling had the mutation in that gene, but the other did not. The study confirmed that the person with the short-sleeper mutation, which can come in numbers of variants, performed better than the twin without the mutation. Still, it is believed that not one but multiple genes are involved.

To sum up, it looks like people’s need for sleep is programmed from birth. Long-sleepers need to sleep a couple of hours more, while short-sleepers feel great and function normally after only a few hours of sleep. Short-sleeper syndrome isn’t considered a sleep disorder, as such people don’t have the problems that insomniacs face – fatigue throughout the day, a need to nap, problems with falling asleep, staying asleep, or waking up frequently throughout the night. No, they just need less time to “clean up” their brains. Additionally, they also tend to be more optimistic and active during the day. Thanks to their syndrome, they can gain anywhere from 30 to even 60 extra days per year! How lucky, especially when compared to those poor long-sleepers. And you, what would you do with such an extra month of free time?

Sleep deprivation and premature mortality risk

Scientists are more and more interested in the physiology of human sleep. In our modern society, people tend to live lives that never stop. We are experiencing a lot of stress: at work, in traffic or even at home. When was the last time you felt your heart pounding in your chest or fear/anger burning deep in your soul? This results in an increase in problems sleeping, sleep deprivation, on a global scale. Doctors are beginning to see the effects of these lifestyle changes. Too little sleep has been already proven to be associated with an increased risk of stroke, coronary heart disease, hypertension, obesity, and type 2 diabetes. In the same way, sleeping for too long is also unhealthy. People who sleep for 8 hours or more have a higher risk of stroke, coronary heart disease, type 2 diabetes, and colorectal cancer.

In a recent metanalysis, it has been shown that sleep deprivation increases the all-cause mortality risk. Metanalysis is a study in which scientists gather the results of many smaller studies to determine an association between two factors with more certainty. In this case, researchers analyzed 35 articles including over 2 400 000 participants in total. You can see the results with our sleep calculator. In the Night-time sleep duration field select the average number of hours you sleep a night (rounded to the closest full hour), and you will see what percentage you are more likely to die prematurely when compared to someone who sleeps 7 hours a day. Makes you think, doesn’t it? Please keep in mind that the data we are using is from adult participants with no cardiovascular disease or cancer. The results may vary for people with these conditions and children.

How to use the sleep calculator?

If you are wondering what time you should go to sleep, try out this sleep cycle calculator. Here is a step-by-step explanation of how to deal with these calculations:

  1. Firstly, check whether your night-time sleep duration puts you at higher mortality risk. Select the number of hours you normally sleep at night. You will see by what percentage you are more likely to “kick the bucket” when compared with a person who sleeps for 7 hours every night.
  2. Now, let’s create a healthy sleeping routine. Take your time to think about your habits: How long does it take for you to fall asleep? Let’s pick 12 minutes for our example.Usually falling asleep takes between 10-20 minutes, so if you’re not sure, leave our default value of 15 mins. However, if you crash out the moment that your head hits the pillow or it takes you an hour or more, account for that as well. These may be symptoms of poor sleep hygiene, but everybody has ups and downs, exhausting days or days with a head full of problems, so if the problem with falling asleep doesn’t happen often, it shouldn’t be a big deal.
  3. Select the time you want to wake up. We’ve chosen to leave 15 minutes time intervals to simplify the calculator display. Assume we want to wake up at 7.15 a.m.
  4. The description below the sleep calculator tells you everything. We’ve included going to bed times with 6 to 1 full sleep cycles, but the first two – 6 and 5 full cycles – are definitely the ones you should aim for.So, for example:
  • If you had a rough day, the best idea would be to go to bed at 10:03 PM – then you’ll sleep for full 6 cycles (9h).
  • Normally, the best option is to lie down at 11:33 PM – that fulfills the 5 cycles condition (7h 30m).
  • For some people, 6 hours sleep is enough – if that’s you, go to bed at 1:03 AM, and you’ll have 4 full cycles of sleep.
  • Other options are not recommended, as 4.5, 3 or 1.5 hours is not enough for us to rest and regenerate, even for elders who needs less sleep than kids or adults.
  1. If you’re wondering what time should you wake up if you go to bed now, we have the answer as well – look at the last paragraph under the sleep calculator and you’ll find the times you should get out of bed to wake up fresh and ready to work.

Apart from using our sleep cycle calculator – which is a great tool, if a bit simplified (it assumes that your sleep cycle is equal to average 90 minutes) – you can try other ways to improve your sleep hygiene, such as this sleep cycle app. The program claims to monitor your sleep patterns and wakes you up in the lightest sleep phase.

Jacek Staszak, Hanna Pamuła, PhD candidate and Kacper Pawlik