Sleep calculator: Figure out your optimal bedtime

Perhaps you’re familiar with the panicky feeling that arises when you look at the clock while you’re in bed at night. You rack your brain as you then calculate how long you have left until your ruthless alarm goes off. It can be very sobering to realise that, once again, you’ve only got a few hours to go. It’s tough enough to fall asleep with that sinking feeling and, in the worse case scenario, it can lead to getting no rest at all.

Moreover, insufficient sleep can have a negative impact on your health. We recommend you use a sleep calculator (ours is great) to determine the ideal time for you to head to bed. That way, you can work your way backwards and adjust your evening routine accordingly, planning in advance for when it’s lights out.

But in order to get the most out of a sleep calculator, it’s crucial to understand what factors influence our bedtime and sleep in general.

Factors that influence bedtime

Sleep isn’t one size fits all. Yet while everyone has different needs, one thing is for sure: Sleeping is essential for our survival and has a large impact on our well-being. A sleep calculator takes general factors into account, such as dividing our sleep into different sleep cycles, as well as individual factors, such as age and sleep type. To better understand which recommendations are right for you, we’ll take a closer look at those individual factors. 

A healthy amount of sleep

It’s impossible to make a blanket a statement about how much sleep is healthy because that number varies from person to person. Your particular genetic makeup determines whether or not you feel well-rested after just 7 hours of sleep or if you’re still feeling drained after a full 8 hours. That said, the National Sleep Foundation, an American nonprofit dedicated to sleep education and advocacy, recommends against both sleeping less than 7 and more than 9 hours, as it “may be compromising [your] health and well-being.”

Ultimately, it's less about the exact amount of hours of sleep you get and more about how you feel the next day. A good night’s sleep is the kind that makes you feel well-rested, refreshed and alert when you wake up in the morning. Maybe you even woke up on your own, a few minutes before your alarm went off. Hooray — and congratulations: That’s your optimal length of sleep. Observe yourself and your needs, and listen to your body.

If you go without enough sleep for a long time, you’re more at risk to develop serious conditions, such as high blood pressure obesity, type 2 diabetes or a disrupted immune system. Excessive sleep is unhealthy too. According to this French survey on nearly 25,000 subjects ages 15-85, sleeping more than 10 hours per day “was associated with psychiatric diseases and higher BMI, but not with other chronic medical diseases.”

Your sleep cycles

When we sleep, our bodies go through several sleep cycles that each consist of different sleep phases or stages. These include the transitional/falling asleep phase, the light sleep phase, the deep sleep phase and the REM sleep phase. (The first three are often grouped together as non-REM sleep phases.)

“REM” stands for "Rapid Eye Movement” because in this phase, our eyeballs move back and forth quickly — a process that’s visible to an onlooker even when our eyes are closed. We often dream very intensely during REM sleep, which is why this sleep phase is also called the dream phase. It usually lasts only a few minutes and then we either wake up very briefly or slip right back into a light sleep.

If you have to wake up, it’s ideal to do it during the period between the end of REM phase and the start of the new sleep cycle, as it will likely be easier to get out of bed. Whereas if we’re woken up by our alarm clock during a deep sleep phase, it can lead to us feeling completely exhausted, no matter how long we’ve been sleeping. This specific wake-up hour can actually be timed out because a sleep cycle typically lasts about 90 minutes on average, which the sleep calculator takes into account too.

Your sleep type

Ever heard of the “morning larks” and the “night owls”? No, we don't mean the animals in the forest; we mean the different sleep types. Each person has a biologically determined internal clock that’s shaped by our sleep type.

There are roughly three categories of sleep types: The early risers, also called larks, who have no problem starting the day early but get easily tired early in the evening; the night owls, who are alive at night but find it difficult to open their eyes in the morning; and then there are those who are somewhere in-between. Your particular sleep type will affect which bedtime is most beneficial for you.

Your age

When you were a baby, you probably slept about a half a day total. (We’ll forgive you for all the times you made it impossible for your parents to catch a mere forty winks...) Then as a teen, sleeping probably wasn’t as important anymore. And as an adult, you probably sleep even less. According to the National Sleep Foundation, newborns need between 14- 17 hours of sleep, which gradually decreases to 8-10 hours by teenage years. For young adults, 7-9 hours is recommended, and then for older adults it’s only 7-8 hours.

Your age is therefore an important factor to take into consideration when using the sleep calculator, as your optimal amount of time in bed might be less than it used to be a couple of years ago.

How fast you fall asleep

The last important factor that a sleep calculator takes into account is the time it typically takes you to fall asleep. After all, placing your head on the pillow doesn't mean you'll conk out immediately and drift off to dreamland. (If only!)

This, too, differs from person to person but it’s also tricky to measure yourself. It’s not like you can keep your eye on the clock, since that would probably keep you from falling asleep anyway. Instead, feel free to use the average time it takes people to fall asleep as your guide: 15 minutes. If you have a feeling that it takes a little longer for you, you can adjust it in the sleep calculator, or try getting to sleep faster with our tips for falling asleep. Another factor that can have a positive effect on reducing the time it takes to fall asleep is practicing good sleep hygiene.

The formula for your sleep calculator

Drum roll, please... It’s time for the moment you’ve been waiting for: calculating your custom optimal bedtime. Our sleep calculator takes several variables into account, each of which you should input according to your personal preferences and attributes:

a = the ideal time you’d like to wake up

b = the ideal number of hours you’d like to sleep

Note: Choose between increments of 90 minutes (6 hours, 7.5 hours or 9 hours) depending on your age and personal experience with how long you need to sleep in order to feel at your best the morning after.

c = the time it typically takes you to fall asleep

Note: the average is 15 minutes

Once you’ve determined these three values, you can plug them into this formula and subtract using the hours on a clock to calculate your optimal bedtime (x).

a - b - c = x

Here’s a handy chart with some sample bedtimes in green, based on a few common times many people tend to wake up.

Wake-up time	6 hours of sleep	7.5 hours of sleep	9 hours of sleep
06:00	23:45	22:15	20:45
07:00	00:45	23:15	21:45
08:00	01:45	00:15	22:45
09:00	02:45	01:15	23:45

What bedtime did the formula calculate for you? Feel free to try it out over the next few days — and change it up a bit to really identify your ideal sleep length. If you get enough sleep but you still feel like you’re in a funk when you wake up, it might be because you’re an owl sleep type. In this case, your early morning performance might naturally be lower than later in the day, so you might want to push your wake-up time back, rather than reduce the number of hours of sleep you get.

Wishing you happy computing — and a good night's sleep too!

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