How long is a sleep cycle? The 90-minute rule, explained
An adult sleep cycle lasts about 90 minutes on average, but anywhere from roughly 70 to 120. Most people go through 4 to 6 cycles a night.
- How long: an adult sleep cycle lasts about 90 minutes on average, but a single cycle can run from roughly 70 to 120 minutes.
- How many: most adults go through 4 to 6 cycles a night, and a 7 to 9 hour night holds about five or six of them.
- What is in one: each cycle moves through light sleep (N1 and N2), deep sleep (N3) and then REM, the stage where most vivid dreams happen.
- How they change: cycles early in the night hold the most deep sleep, while REM periods grow longer toward morning.
- The 90-minute rule: it is a useful average, not a fixed clock; a study that recorded healthy people for four nights found that cycles differed far more from person to person than from night to night.
Shimmr Binaural beats for meditation, sleep and focus Get Shimmr How long is a sleep cycle? For an adult, about 90 minutes on average, though one cycle can last anywhere from roughly 70 to 120 minutes. You go through 4 to 6 of them each night. Here is what happens inside a cycle, how the night changes from the first one to the last, and how much to trust the popular 90-minute rule.
How long is a sleep cycle?
An adult sleep cycle lasts about 90 minutes on average. That number is an average across many people and many cycles. Real cycles vary from roughly 70 to 120 minutes, the first cycle of the night is often shorter, and later ones can be longer.
A cycle ends with a short stretch of light sleep or REM, and many people wake for a few seconds before the next one begins. Most of those wakings are forgotten by morning. When one does stick, it often happens in the early hours, which is why so many people find themselves waking up at 3am.
What are the stages of a sleep cycle?
Each cycle moves through four stages, three of non-REM sleep and then REM sleep:
| Stage | What it is | Brain waves |
|---|---|---|
| N1 | Drifting off, a few minutes, easy to wake | Theta, 4 to 8 Hz |
| N2 | Light sleep, about half the night in total | Theta with short bursts called spindles |
| N3 | Deep sleep, hardest to wake from | Slow delta waves, 0.5 to 4 Hz |
| REM | Dreaming sleep, eyes move, body is still | Fast, mixed, close to waking |
After N3 you usually rise back through N2 into REM. REM is where most vivid dreams happen, and your muscles relax so you do not act them out.
How does the sleep cycle change through the night?
The first half of the night holds most of your deep sleep, and the second half holds most of your REM. Early cycles have long stretches of N3. As the night goes on, N3 shrinks and REM periods grow, so the last cycle before you wake can hold a REM period of 30 minutes or more.
Age changes the picture too. A 2004 meta-analysis of 65 studies covering 3,577 healthy people aged 5 to 102 found that in adults, the share of deep sleep and of REM sleep went down with age, while light sleep and time awake after falling asleep went up. If you want more of the first kind, our guide to deep sleep covers what helps.
How many sleep cycles do you need?
Most adults go through 4 to 6 sleep cycles a night, and the 7 to 9 hours most adults need holds about five or six. Five cycles of 90 minutes come to 7.5 hours, which is why that number appears so often. Your body cares about the total amount of sleep, and about getting enough deep sleep and REM, more than about an exact count of cycles.
Should you time your sleep by 90-minute cycles?
You can use 90 minute blocks as a rough guide, but not as an exact clock. The idea is simple: count back from your wake-up time in 90 minute steps, then add about 15 minutes to fall asleep. For a 7am alarm, that looks like this:
| Cycles | Sleep | Go to bed around |
|---|---|---|
| 6 | 9 h | 9:45pm |
| 5 | 7.5 h | 11:15pm |
| 4 | 6 h | 12:45am |
The catch is that your cycles are your own. In a 2001 study, healthy people had their sleep recorded at home for four nights in a row. Differences in the number and length of cycles between nights were far smaller than the differences between people. People whose first REM period came sooner tended to have more cycles, each one shorter. A 2020 review notes that what sets the number and length of cycles each night is still an open question.
So try the table, and adjust it. If you often wake groggy, move your bedtime by 15 to 20 minutes and see how the next week feels.
Is a 90-minute nap a full sleep cycle?
For many people, roughly yes. A 90 minute nap gives you about one full cycle, including some deep sleep and some REM, and you are more likely to wake from lighter sleep at the end. A short nap of 10 to 20 minutes stays in N1 and N2, so it is easy to wake from. Naps of around 30 to 60 minutes are the ones most likely to leave you groggy, because they often end in deep sleep. Our guide to the power nap goes into timing in more detail.
In Shimmr, the Awake → Asleep Shift glides from Alpha down to Delta over 20 to 90 minutes, about one sleep cycle at its longest, and the Power Nap soundscape suits shorter rests. Set the sleep timer and the sound fades out on its own. Shimmr has no alarm, so use your phone’s clock to wake.
Common questions
How long is one sleep cycle?
About 90 minutes on average for an adult. Individual cycles vary from roughly 70 to 120 minutes, and the first one of the night is often a little shorter.
How many sleep cycles do you need?
Most adults go through 4 to 6 cycles a night, and the 7 to 9 hours most adults need holds about five or six. The total amount of sleep matters more than hitting an exact number of cycles.
Is it better to wake up at the end of a sleep cycle?
Waking from light sleep usually feels easier than waking from deep sleep, so many people prefer it. Because cycle length varies, a bedtime counted in 90 minute blocks is a rough guide, not a guarantee.
What are the stages of a sleep cycle?
A cycle goes through N1 (drifting off), N2 (light sleep), N3 (deep sleep) and REM (dreaming sleep). Short wakings between cycles are normal and usually forgotten.
Is a 90-minute nap a full cycle?
For many people, roughly yes: 90 minutes is about one full cycle, so you are more likely to wake from lighter sleep. A short nap of 10 to 20 minutes avoids deep sleep altogether.
From Gareth, who makes Shimmr This article is for general information and is not medical advice. Binaural beats are not a treatment for insomnia or any other condition.