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Do you sometimes wake up groggy? Waking up on the wrong side of the bed may be less about how much shuteye you get and more about where you are in your sleep cycle when you awaken. Humans experience multiple cycles while asleep, and waking in the middle of the wrong one could cause drowsiness. Therefore, you should know how much rest you need to avoid waking mid-cycle, and the good news is we are here to help. We’ll walk you through how to use our sleep calculator to maximize your rest. Plus, we’ll go over what happens while you sleep, why quality rest is important, and more.

Stages of Sleep

There are four stages of sleep [1], and they are divided into two phases, rapid eye movement (REM) and non-rapid eye movement (non-REM). The first three stages involve non-REM sleep, while the fourth and final stage is REM sleep. During a cycle, you will move through each of these four stages, starting with Stage 1 of non-REM slumber and ending with REM. Therefore, to finish a full cycle, you need to complete all four stages. Once you are done with REM, you then move on to another cycle, repeating this pattern throughout the night. Each cycle lasts for about 90 to 110 minutes.

What Happens During Each Stage

Stage 1 is a light rest lasting roughly 5 to 10 minutes. During this time, your eye movement slows, and your muscles start relaxing. You may also experience hypnic jerking, a sudden muscle contraction. The second stage is when your brain waves and heart rate slow down, body temperature drops, and eye movement ceases. The second stage typically lasts 10 to 25 [2] minutes. You are in a deep slumber during the third non-REM stage, and you’re likely to feel disoriented if awakened. Furthermore, you generate very slow brain waves, which is why this stage is also known as slow-wave. Lastly, you have no eye or muscle movement.

Rem Cycle - The Most Important One

The final stage, REM, is when your brain waves begin to quicken again as you leave deep sleep. Your heart rate and blood pressure also start to rise, and your breathing becomes more rapid. As the name suggests, this stage is marked by faster eye movements as well. REM is also when people usually dream. To avoid physically acting out these dreams, though, your legs and arms remain in a state of paralysis. According to Valley Sleep Center [3], REM is highly important because it “stimulates the areas of your brain that are essential in learning and making or retaining memories.” As you cycle through multiple REM stages during the night, they will first last around 10 minutes and then get increasingly longer. The amount of REM slumber you need depends on your age. For example, babies and young children need the most, and this amount decreases as you move into adolescence and adulthood.

How to Use Sleep Calculator

The calculator is designed to help you wake up during Stage 1, the lightest rest. There are three ways to use this calculator to generate your custom bedtime duration. The first option is to input the time you need to wake up. The tool will then provide you with recommended bedtimes. The second option is to input that you’d like to go to bed right now, and the calculator will show you when to wake up. Thirdly, you can choose to input when you’d like to go to bed later that night, and the tool will give you recommended wake-up times.

The Effects of Sleep Deprivation on Your Body

Insufficient rest can have a significant impact on your well-being. Not only can it impair your physical health, but it can also affect your emotional and cognitive health. One of the primary effects of inadequate shuteye is daytime fatigue. Furthermore, feeling too tired during the day increases your chances of getting into an accident. According to Johns Hopkins Medicine [4], 6,000 fatal car crashes each year are due to drowsy driving. Other physical ramifications include an increased risk of illness, heart disease, high blood pressure, obesity, colorectal cancer, and type 2 diabetes. Poor rest is also linked to an increased of dementia, negative moods, and difficulty concentrating.

How to Improve Your Sleep Quality

If you feel like your slumber is subpar, you can do things to promote better rest. The first tip is to maintain a consistent bedtime and wake-up time, including weekends. The great news is you can use the calculator to help determine your ideal schedule and then stick to that. Secondly, avoid alcohol, caffeine, and nicotine as they can disrupt your rest. Furthermore, going to bed full or hungry can also affect your rest. If you take naps, don’t doze off too late in the day or for more than 30 minutes. Physical activity should also help you rest better, so consider going out for a run or walk if you need an afternoon recharge. Make sure your bedroom is conducive to quality rest by keeping it cool, quiet, and dark. Lastly, help alleviate stress that can keep you up by establishing a relaxing nightly routine before bed, such as reading a book or drinking hot tea.

Frequently Asked Questions

How many hours of sleep is recommended?

Although the calculator can help you wake up during a lighter slumber, that’s not to say you should actively pursue fewer hours of shuteye than recommended by the medical community. Experts suggest that adults get between 7 and 9 [5] hours of slumber each night, which correlates to 5 or 6 full cycles. However, this amount can vary depending on your health and personal circumstances. For instance, if you are recovering from a cold, you will likely doze off longer than you would normally. Babies, children, and teens should get even more slumber. For example, a newborn baby needs between 14 and 17 hours of shuteye.

Is it normal to still feel tired after sleeping for 8 hours?

Yes, you can sleep for 8 hours and still feel tired. Even though you got the amount of rest that health experts recommend, you likely woke up toward the end of a sleep cycle. The length of these cycles can vary. We mentioned earlier that a complete cycle could last from 90 to 110 minutes. The duration of each stage can vary too, further affecting the cycle duration. Each person is different, and therefore, you cannot count down a cycle to the exact minute. Instead, these numbers represent a general observation from health experts to help people better understand how we rest.


If you want to wake up more refreshed, the sleep calculator could be the solution of your dreams. While people rest, they move through four stages. The first three are non-REM, and the fourth is REM. Together, these four stages are a full cycle. The ideal time to wake up is during the first and lightest stage, and experts suggest adults get between 5 and 6 cycles, equating to 7 to 9 hours of shuteye. Along with the calculator, you can implement good habits to further improve your slumber. Your doctor will also thank you for prioritizing your sleep since this is vital to keeping your health in check.

  • Cleveland Clinic. Sleep Basics. Last modified December 7, 2020.
  • Harvard Medical School. Natural Patterns of Sleep. Last modified December 18, 2007.
  • Valley Sleep Center. 3 Things You Should Know About REM Sleep. Last modified February 13, 2020.
  • Johns Hopkins Medicine. The Effects of Sleep
  • Cleveland Clinic. How Much Sleep Do I Need?. Last modified February 25, 2021.