Wake up refreshed by aligning with your 90-minute sleep cycles.
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Assumes 15 min to fall asleep · 90-min sleep cycles · 5–6 cycles recommended
Woke up in a bad mood? Feeling tired in the morning? Pressed the snooze button one too many times and now you’re late to work? If these scenarios seem familiar, your sleep routine may be the problem and a sleep calculator the solution.
In a 2012 World Health Organization study of more than 40,000 individuals from eight countries, over 16% of participants reported severe sleep problems. WHO warned that sleep problems may become a global epidemic. Another study published in JAMA Network Open evaluated the sleep habits of US adults between 2017 and 2020 and found that almost 30% experienced at least 1 hour of sleep debt.
How come we fail at performing one of the body’s basic functions? Our busy lifestyles (and the invention of the alarm clock) have disrupted our circadian rhythms. We can no longer afford to go to sleep when we feel sleepy and wake up naturally at the end of a sleep cycle. We also underestimate sleep and rest based on how many hours we want to spend sleeping, rather than how many hours the body actually needs. That’s why we need a sleep calculator: to remind us that some bodily functions are non-negotiable and to restore balance and well-being to our lives.
A sleep calculator is a tool that helps you calculate bedtime and wake-up time based not only on how many hours you want to sleep but also on sleep cycles. The idea behind a sleep calculator is to avoid waking up mid-sleep cycle, as your body would naturally wake up. Waking up at the end of a sleep cycle reduces sleep inertia (you wake up and clear your mind faster), makes you fresher and more energetic, and improves your morning mood.
During sleep, your brain performs the same recurring tasks in cycles of about 90- 120 minutes. It goes through stages, from light sleep to deep sleep to a near-awake stage, but varies the length of each stage from one sleep cycle to another. That’s why the length of sleep is as important as the moment you wake up. Here’s what happens when you sleep.
The first phase of a sleep cycle is a light sleep or a dozing-off phase, when your body relaxes and transitions from being awake to being asleep. It usually lasts between one and seven minutes. If you wake up during this phase, you may not even know you were asleep. The first phase is longer during the first sleep cycle and shorter during subsequent cycles.
The second phase of a sleep cycle is a deeper sleep stage, part of a larger stage called non-rapid eye movement (non-REM) sleep. During this stage, you are asleep, but not too deeply. Your heart rate and body temperature are lower, and your body is relaxed. You are shielded from noise and less likely to wake. The non-REM stage lasts somewhere between 10 and 25 minutes. It’s shorter during the first sleep cycle and increases with each following cycle.
The third phase of a sleep cycle is a deep sleep stage, also part of the non-REM stage. During this phase, which lasts between 20 and 40 minutes, you are deeply asleep and rest well. Your brain is unaware of the outside world and is focused on regulating your body (e.g., repairing tissue, consolidating memory, regulating hormones and the immune system). You don’t want to wake up during the third phase.
The fourth and last phase of a sleep cycle is called rapid eye movement (REM). It lasts between 10 and 60 minutes, shorter during the first sleep cycle of the night and longer during the morning ones. In this stage, your brain is almost awake, which explains the appearance of dreams.
An REM and non-REM sleep calculator helps you determine bedtime and waking up time to avoid disturbing the REM and non-REM stages of your sleep cycles. On average, the total duration of the two non-REM stages and the REM stage is about 90 minutes.
So, if you must wake up at a certain time T to go to work, you must be asleep between T and T - 90 minutes, T - 90 minutes and T - 180 minutes, T - 180 minutes and T - 270 minutes, and so on.
For example, if you set the alarm at 7:00 AM, you must go to bed at 5:30 AM to sleep one sleep cycle, at 4:00 AM to sleep two sleep cycles, at 2:30 AM to sleep three cycles, at 1:00 AM to sleep four cycles, or at 11:30 PM to sleep five cycles.
The same formula applies when you know the bedtime and want to calculate the waking up time. Going to bed at 11:00 PM means you can wake up after one sleep cycle at 00:30 AM, after two cycles at 2:00 AM, after three cycles at 3:30 AM, after four cycles at 5:00 AM, or after five cycles at 6:30 AM.
Of course, these are just theoretical examples. In practice, your body needs much more than one sleep cycle, as we’ll discuss later on.
Sleep time is fundamental for your health and well-being. Sleep duration and quality impact your whole body, from metabolic functions (e.g., cardiovascular, immunity, and cognition) to mood and psychological health. Sleep regulates hormones, tissue repair, memory consolidation, and brain detoxing.
At the same time, knowing when to go to sleep and when to wake up based on sleep cycles optimizes your chances of getting a good night's sleep and waking up refreshed and happy. Improving your sleep routine and creating healthy sleep patterns go a long way. Furthermore, you will get used to it pretty quickly and only need to rely on a sleep cycle calculator when you change your routine (e.g., traveling to a different time zone, changing your work schedule, working night shifts, etc.).
Published in 2015, the National Sleep Foundation’s sleep time duration recommendations are as follows:
Age | Recommended sleep time duration (hours) | May be appropiate sleep time duration (hours) | Not recommended sleep time duration (hours) |
0 - 3 months | 14 - 17 | 11 - 13 / 18 - 19 | Less than 11 / More than 19 |
4- 11 months | 12 - 15 | 10 - 11 / 16 - 18 | Less than 10 / More than 18 |
12- 24 months | 11 - 14 | 9 - 10 / 15 - 16 | Less than 9 / More than 16 |
3 - 5 years | 10 - 13 | 8 - 9 / 14 | Less than 8 / More than 14 |
6- 13 years | 9 - 10 | 7 - 8 / 12 | Less than 7 / More than 12 |
14- 17 years | 8 - 10 | 7 / 11 | Less than 7 / More than 11 |
18- 25 years | 7 - 9 | 6 / 10 - 11 | Less than 6 / More than 11 |
25- 64 years | 7 - 9 | 6 / 10 | Less than 6 / More than 10 |
Over 65 years | 7 - 8 | 5 - 6 / 9 | Less than 5 / More than 9 |
These are the general recommendations, but how many hours of sleep each individual needs depends on more factors than just age. For instance, factors such as overall health (e.g., during illness, the body may need more time for recovery and repair), pregnancy, gender, recovery after sleep deprivation, physical effort, stress, and even genetics influence your sleep duration.
Besides the age categories specified by the National Sleep Foundation, you may experience shifts in your sleep duration within an age category. If you notice you struggle to fall asleep, wake up before the alarm, experience daytime drowsiness, rely on caffeine to get you through the morning, or wake up during the night, you may consider adjusting your sleep duration.
The easiest way is to take a few days to allow your body to fall asleep and wake up naturally, then determine how many hours of sleep you got. Even a small 30-minute difference may have a big impact on your well-being.
The healthiest way of regulating your circadian cycle is to follow natural light: go to bed when it gets dark and wake up when the sun is up. However, that’s not really feasible nowadays. What’s feasible is to find a sleep schedule you can sustain consistently without disrupting your lifestyle or affecting your health and to consider natural light as much as possible.
For instance, you may feel more energetic during summer evenings when you benefit from more natural light and more droopy during winter evenings when you have less natural light. If possible, adjust your sleeping schedule accordingly.
If going to bed is more or less dictated by natural light and season, waking up time is dictated by completing sleep cycles. Try to schedule the alarm to accommodate a full sleep cycle. If the morning routine is important to you, set up the alarm 90 minutes earlier and go to bed 90 minutes earlier, too.
Your health depends on the duration and quality of your sleep. You simply can’t function properly or at length without getting enough sleep, and the effects of sleep deprivation aren’t limited to feeling drowsy and tired. Sleep deprivation has serious consequences on your body and mind.
A healthy and consistent sleep routine is key to your well-being. It encompasses not only using a sleep calculator to determine the optimal bedtime or wake-up time, but also ensuring you get enough sleep and a cool, dark, quiet, and comfortable environment. You also want consistency so your body can get used to a routine and adopt it naturally. Of course, when the routine is broken, you need to allow your body to rest and recover. Here are some tips to improve your sleep:
The sleep calculator allows you to personalize both your bedtime and wake-up time, so you know at any moment what the ideal time is to get the most out of your sleep routine and wake up fresh and energized.
Sleep is not an indulgence. It is a necessity. Getting enough sleep and having good sleep quality is the foundation of your day. It dictates how you show up in the world, your work performance, the quality of your relationships, your creativity and decision-making process, and your mood. And getting enough sleep is not all that matters. You need a sleep cycle calculator to tell you when to go to bed or wake up to optimize your sleep and wake up happier, full of energy, and ready for whatever life has in store for you. Sleep well!
[1] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0071292