How to Calculate When You Should Go to Sleep

How much sleep you need changes throughout your lifetime. An infant may need up to 17 hours of sleep each day, while an older adult may get by on just 7 hours of sleep a night.

Sleep guidelines can offer a place to start determining your sleep needs by providing research-backed recommendations for the ideal amount of sleep for optimal health.

The American Academy of Pediatrics and the Centers for Disease Control and Prevention (CDC) offer these general guidelines for different age groups:

Keep in mind, though, that sleep needs can still vary, even within the same age group.

You might need at least 9 hours of sleep a night to feel well rested, while your partner may wake up naturally after 7 hours, feeling perfectly refreshed and ready for the day.

The thing to keep in mind is how you feel when you get various amounts of sleep.

Here are a few questions to consider when evaluating your sleep needs:

• Do I feel rested after 7 hours of sleep, or do I need at least 8 or 9?
• Do I experience any daytime drowsiness?
• Do I rely on caffeine to keep me going throughout the day?
• Has my sleeping partner noticed me tossing and turning, or having any sleep issues during the night?

Bedtimes are based on:

• your wake-up time
• completing five or six 90-minute sleep cycles
• allowing 15 minutes to fall asleep

Sleep deprivation is a real concern for many people, especially those faced with consistent work and life challenges that can further disrupt sleep.

Of course, getting too little sleep can affect many of your body’s systems and restorative functions.

Health and mental health concerns — depression, anxiety, obstructive sleep apnea, and chronic pain, just to name a few — can contribute to sleep deprivation. But a lack of quality sleep can also worsen symptoms of these conditions and fuel a distressing cycle of sleeplessness.

The occasional night of poor sleep generally won’t have a serious impact on your health. All the same, experts have linked ongoing sleep deprivation to serious health consequences, including a higher risk of chronic diseases and early death.

Sleep deprivation can have short-term and long-term physical, emotional, and cognitive health impacts.

Physical impacts

For most people, a night of poor sleep can bring on noticeable physical effects, including:

• drowsiness
• headache
• dark circles under the eyes
• pale skin

Long-term sleep deprivation can take a more severe toll on your physical health, leading to:

• reduced immunity, which can make it harder for your body to fight off infections
• high cortisol, which can contribute to high blood pressure and other health concerns
• increased appetite and cravings for sugar and carbs
• changes in weight
• signs of aging, including wrinkles, fine lines, and loss of skin elasticity
• chronic inflammation

Emotional and mental health impacts

Without a doubt, a night of bad sleep can affect your mood the next day.

When you don’t get enough sleep, you’re more likely to:

• feel cranky and irritable
• notice abrupt mood changes and difficulty managing emotions
• have difficulty coping with stress

Research also suggests that sleep deprivation can worsen mental health symptoms, including depression, anxiety, paranoia, and hallucinations.

Sleep deprivation has also been linked to symptoms of some mental health conditions, including:

• depression
• anxiety disorders
• bipolar disorder
• attention deficit hyperactivity disorder (ADHD)

Cognitive impacts

When you don’t get enough sleep, your brain can’t work as efficiently. As a result, you’ll likely have trouble concentrating and remembering things after a night of poor sleep.

Research has found evidence to suggest that sleep deprivation negatively affects functions associated with the brain’s frontal lobe, including:

• attention
• alertness
• decision making
• judgment
• memory
• response

These effects can play a part in:

• declining performance at work or school
• changes in judgment and impulse control
• accidents

When you fall asleep, your brain and body go through several cycles of sleep. Each cycle includes four distinct stages.

• The first three stages are part of non-rapid eye movement (NREM) sleep.
• The last stage is rapid eye movement (REM) sleep.

The stages used to be classified as stages 1, 2, 3, 4, and REM. Now, experts generally classify them as:

• N1 (formerly stage 1). This first stage of sleep marks the period between being awake and falling asleep.
• N2 (formerly stage 2). The onset of sleep begins at this stage, as you become unaware of your surroundings. Your body temperature drops slightly, and your breathing and heart rate become regular.
• N3 (formerly stages 3 and 4). During this deepest and most restorative sleep stage, breathing slows, blood pressure drops, muscles relax, hormones are released, healing occurs, and your body becomes re-energized.
• REM. This final stage takes up about 25 percent of your sleep cycle. During REM sleep, your brain is most active, dreams occur, and your eyes move back and forth rapidly under your eyelids. REM sleep helps boost your mental and physical performance when you wake up.

It takes, on average, about 90 minutes to go through each cycle. Completing five cycles a night means you’d get 7.5 hours of sleep, while six full cycles translates to about 9 hours of sleep.

Ideally, you want to wake up at the end of a sleep cycle instead of in the middle of it — that’s because you’ll typically feel more refreshed and energized if you wake up at the end of a cycle.

Sleep is crucial for many reasons. A good night’s sleep:

• helps regulate the release of hormones that control appetite, metabolism, growth, and healing
• boosts brain function, concentration, focus, and productivity
• reduces your risk for heart disease and stroke
• helps with weight management
• helps maintain healthy immune system function
• lowers your risk for chronic health conditions, such as diabetes and high blood pressure
• improves athletic performance, reaction time, and speed
• may lower your risk for depression
• improves libido and sexual function

You’ll find answers to some common questions about sleep below.

Does your need for sleep change with age?

Yes, your need for sleep does change with age, though it typically stabilizes around the age of 20.

As you get older, you need less sleep, as a general rule.

Various environmental, behavioral, and medical factors can influence how much sleep you need, though, and those may change throughout your life.

For instance:

• A young adult may want to do more — and stay up later — than they could as a teenager.
• An adult in their 40s has a higher chance of chronic health conditions that might affect their sleep needs.
• Changing lifestyles in older age, including an irregular schedule, may lead to more time spent in bed.

Why am I still tired after sleeping for 8 hours?

There are a few possible reasons you might wake up tired, even after sleeping for 8 hours. A good place to start exploring these reasons? Consider your sleep habits and sleep hygiene practices.

When it comes to sleep, quality matters just as much as quantity. Things that could detract from the quality of your sleep include:

• your sleep environment (Is it noisy? Too hot or cold? Too bright?)
• who you share your bed with (A partner who snores or fidgets? A restless pet?)
• sleep disorders like insomnia or sleep apnea
• chronic pain
• an underlying medical or mental health condition

Is it healthy to sleep during the day?

Pulling all-nighters, or working the graveyard shift and then sleeping in the day, may contribute to some negative health effects, including increased risk for cardiovascular disease and type 2 diabetes.

Research suggests that being a night owl could also affect your eating habits and lead to erratic eating patterns, including:

• skipping breakfast and overeating later in the day
• consuming more sugar, caffeine, alcohol, and fast food

What’s more, getting quality sleep during the day can be a challenge, with all the distractions and noise of life happening around you.

When you don’t have any option beyond working at night and sleeping during the day, these tips can help you get better rest.

To improve your sleep health, consider the following tips.

During the day

• Exercise regularly, but try to schedule your workouts at least a few hours before you go to sleep. Exercising too close to bedtime may lead to interrupted sleep.
• Increase your exposure to sunlight or bright lights during the day. This can help maintain your body’s circadian rhythms, which affect your sleep-wake cycle.
• Try not to take long naps, especially late in the afternoon.
• Try to wake up at the same time each day.

Before bed

• Limit alcohol, caffeine, and nicotine in the evening. These substances have the potential to interrupt your sleep or make it difficult to fall asleep.
• Switch off electronics at least 30 minutes before bedtime. The light from these devices can stimulate your brain and make it harder to fall asleep.
• Get into the habit of a relaxing routine before bedtime, like taking a hot bath or listening to soothing music.
• Turn down the lights shortly before bedtime to help your brain understand that it’s time to sleep.
• Turn down the thermostat in your bedroom. 65°F (18.3°C) is an ideal sleeping temperature.

In bed

• Avoid screen time in bed to reduce blue light exposure, which can disrupt sleep.
• Read a book or listen to white noise to help you relax.
• Close your eyes, relax your muscles, and focus on steady breathing.
• If you’re unable to fall asleep, get out of bed and move to another room. Read a book or listen to music until you start feeling tired, then go back to bed.

For more sleep support, check out our sleep shop.

If you’re aiming for 7 to 9 hours of sleep each night, a sleep calculator (like the one above) can help you figure out what time to go to bed based on your wake-up time.

Ideally, you’ll want to wake up at the end of your sleep cycle, which is when you’re most likely to feel the most rested.

A good night’s sleep is essential to good health, so if you’re having trouble falling asleep or staying asleep, consider reaching out to a healthcare professional. They can help you explore underlying causes of sleep difficulties and offer guidance.