Sleep research has shown that we go through the various light/deep/REM sleep states in a fairly consistent 90-minute cycle. This 90-minute pattern is closely linked to our circadian rhythms, our inbuilt body clock that naturally determines our wakefulness and sleepiness.
The 90 Minute Rule involves working on an activity for a maximum of 90 minutes then taking a break by physically and mentally moving away from the task that you have been working on.
An average sleep cycle lasts about 90 minutes. Ideally, you need four to six cycles of sleep every 24 hours to feel fresh and rested. Each cycle contains four individual stages: three that form non-rapid eye movement (NREM) sleep and one rapid eye movement (REM) sleep.
During a typical night, your sleep alternates through cycles of REM and NREM sleep about every 90 minutes. The REM stage accounts for approximately 25 percent of sleep time, while the NREM stage takes up the other 75 percent.
If your school or work schedule requires you to be up between 5:00 and 7:00 a.m., these are the suggested bedtimes: School-age children should go to bed between 8:00 and 9:00 p.m. Teens should try to go to bed between 9:00 and 10:00 p.m. Adults should try to go to sleep between 10:00 and 11:00 p.m.
Scientists agree that sleep is essential to health, and while stages 1 to 4 and REM sleep are all important, deep sleep is the most essential of all for feeling rested and staying healthy.
Ideally, you should try to get more than 90 minutes of sleep. Sleeping between 90 and 110 minutes gives your body time to complete one full sleep cycle and can minimize grogginess when you wake. But any sleep is better than not at all — even if it's a 20-minute nap. For more sleep support, check out our sleep shop.
You can figure out the best bedtime for your schedule based on when you have to wake up in the morning and counting backward by 7 hours (the recommended minimum per night for adults). For example, if you need to be up by 6 a.m., you should consider winding down before 11 p.m.
How to work out the ideal bedtime. If you need to wake up by 7am then count back 7.5 hours to find that bedtime is around 11.30pm. Make sure you're in bed before then so you're relaxed ready for sleep and allow yourself 15 minutes to drop off. You can use the sleep calculator to find the ideal bedtime for you.
Your brain can only focus for 90 to 120 minutes before it needs a break, Widrich reports. Why? It's the ultradian rhythm, a cycle that's present in both our sleeping and waking lives. As Tony Schwartz has reported, this was first discovered by Nathan Kleitman, a groundbreaking sleep researcher.
Although there is some genetic variation, most adults need between 7.5 to 8.5 hours of sleep per 24-hour period to function optimally. You can find your optimal sleep time if you set aside several days (perhaps during a vacation) to allow yourself to sleep as long as possible.
3 hours before bed: No more food or alcohol. 2 hours before bed: No more work. 1 hour before bed: No more screen time (shut off all phones, TVs and computers). 0: The number of times you'll need to hit snooze in the AM.
Rapid eye movement (REM) sleep, or stage R, usually starts about 90 minutes after you fall asleep. Brain activity increases, your eyes dart around quickly, and your pulse, blood pressure, and breathing speed up. This is also when you do most of your dreaming. REM sleep is important for learning and memory.
If you nap in the morning, the sleep consists primarily of light NREM (and possibly REM) sleep. In contrast, napping later in the evening, as your sleep drive increases, will comprise more deep sleep. This, in turn, may disrupt your ability to fall asleep at night. Therefore, napping late in the day is discouraged.
In general, the best nap length for adults is about 20 minutes and no longer than 30 minutes. Sleeping for 20 minutes allows the napper to get a bit of light sleep to boost alertness without entering into deep sleep. Waking up from deep sleep can cause grogginess and actually worsen sleepiness.
Sleep needs can vary from person to person, but in general, experts recommend that healthy adults get an average of 7 to 9 hours per night of shuteye. If you regularly need more than 8 or 9 hours of sleep per night to feel rested, it might be a sign of an underlying problem, Polotsky says.
10pm is the perfect bedtime. Going to sleep at 10pm enables you to get the recommended 7–8 hours of sleep, and still wake up by 5 or 6am. That means you can get in at least a 30-minute workout in the morning — a common habit among the most successful and productive people — and still be at work by 8 or 9am.
But the majority manage to get at least 6 hours, as you can see in the list below detailing the sleep habits of 10 highly successful people: Elon Musk, CEO of Tesla and SpaceX: 6 hours (1am — 7am) Tim Cook, CEO of Apple: 7 hours (9:30pm — 4:30am) Bill Gates, Co-Founder of Microsoft: 7 hours (12am — 7am)
“There is no such thing as a “fixed or ideal time” to go to bed which will suit all individuals. It is generally advisable to fall asleep between 10 pm to midnight as for most people this is when the circadian rhythm is at a point that favours falling asleep.”
There are several reasons that you might not be getting enough deep sleep. Weakened sleep drive. Taking naps or spending too much time in bed can weaken your sleep drive. You may lose some of your ability to sleep normally, and as a result, you may get less deep sleep.
The takeaway.
Spending around 90 minutes in REM sleep each night is considered healthy for most adults, though it depends on the person.
For healthy adults, spending 20-25% of your time asleep in the REM stage is a good goal. If you get 7-8 hours of sleep, around 90 minutes of that should be REM.