Sleep Calculator
Find bedtimes and wake-up times that line up with your natural 90-minute sleep cycles, so you are more likely to wake up feeling refreshed.
By Khalid Waleed, PhD · Updated October 26, 2026 · Sources
Results
Highlighted times give the recommended amount of sleep for your age. Times include the minutes it takes you to fall asleep.
Use this every night? Install the Sleep Calculator as an app on your phone or computer. It opens in one tap and works offline.
How the sleep calculator works
Sleep is not one long, even state. Through the night you move through repeating cycles of light sleep, deep sleep and REM (dream) sleep. Each cycle lasts roughly 90 minutes on average, although it varies between people and through the night.
Waking at the end of a cycle, when sleep is lighter, often feels easier than being woken from deep sleep. This calculator counts back (or forward) in whole sleep cycles from the time you choose, and adds the time it usually takes you to fall asleep. It uses 90 minutes by default, but you can choose a shorter or longer cycle, because real cycles vary from person to person and lengthen through the night. Tell it your age and it highlights the times that give you the amount of sleep the CDC recommends for your age group. Your settings are remembered on this device, so next time it is ready to go.
| Cycles | Sleep time | Best for |
|---|---|---|
| 6 | 9 hours | Teenagers, recovery, very active days |
| 5 | 7.5 hours | Most adults |
| 4 | 6 hours | An occasional short night |
| 3 | 4.5 hours | Not recommended regularly |
What happens in each sleep cycle?
Each cycle moves through light sleep (stages N1 and N2), deep sleep (N3) and REM sleep, when most vivid dreaming happens. The mix changes through the night: the early cycles hold most of your deep sleep, while REM periods grow longer towards morning. That is one reason a night cut short tends to cost you REM sleep in particular.
Illustration only. Real nights vary from person to person and night to night.
| Stage | What happens | Share of the night (adults) |
|---|---|---|
| N1 (light) | Drifting off; you are easy to wake | About 5% |
| N2 (light) | Heart rate and body temperature drop; the stage you spend most time in | About half |
| N3 (deep) | Hardest to wake from; important for physical recovery | About 15 to 25%, less with age |
| REM | Vivid dreams; linked to memory and emotional processing | About 20 to 25% |
How much sleep do you need by age?
| Age | Recommended sleep (CDC) |
|---|---|
| Teens (13 to 17) | 8 to 10 hours per 24 hours |
| Adults (18 to 60) | 7 or more hours a night |
| Adults (61 to 64) | 7 to 9 hours |
| Adults (65 and over) | 7 to 8 hours |
If you regularly need an alarm to drag yourself awake or feel sleepy during the day, you may need more sleep than you are getting. Our Sleep Debt Calculator shows how much you are missing each week. For more detail, read how many hours of sleep you really need and how much sleep women need.
What time should I go to bed? Quick bedtime chart
These bedtimes allow 15 minutes to fall asleep and end on a full 90-minute cycle. Five cycles (7.5 hours) suits most adults; six cycles (9 hours) suits teenagers and anyone catching up on sleep.
| Wake-up time | Bedtime for 5 cycles (7.5 h) | Bedtime for 6 cycles (9 h) |
|---|---|---|
| 5:00 AM | 9:15 PM | 7:45 PM |
| 6:00 AM | 10:15 PM | 8:45 PM |
| 6:30 AM | 10:45 PM | 9:15 PM |
| 7:00 AM | 11:15 PM | 9:45 PM |
| 7:30 AM | 11:45 PM | 10:15 PM |
| 8:00 AM | 12:15 AM | 10:45 PM |
Need a different time, or take longer to fall asleep? Use the calculator above for a personalised result.
Woke up groggy or between cycles?
Some grogginess after waking, called sleep inertia, is normal and usually fades within about 15 to 30 minutes. Opening the curtains, getting into bright light and moving around help it pass faster. If you often wake up groggy at your calculated times, try a different cycle length in the calculator for a week, and check that you are getting enough total sleep: being short on sleep makes grogginess worse whatever time you wake. If you wake naturally a little before your alarm and feel alert, it is usually fine to get up.
Can I use this calculator for naps?
Naps work a little differently. For a quick boost, a 10 to 20 minute nap avoids deep sleep and the grogginess that comes with it, while a nap of about 90 minutes lets you complete a full cycle. Our guide to how long a nap should be explains which length suits which situation, and why it is best to nap before about 3 p.m.
Tips for using your results
- Keep the same wake-up time every day, including weekends. It is one of the most effective ways to improve sleep.
- Start winding down 30 to 60 minutes before your bedtime, with dim lights and no work.
- Avoid caffeine in the 8 hours before bed.
- If you cannot fall asleep after about 20 minutes, get up, do something calm in low light, and return when sleepy.
For a simple evening plan, see our 90-minute bedtime routine, and check how long caffeine stays in your system. Want to see what affects your sleep? Read our guide to keeping a 2-week sleep diary.
Frequently asked questions
Is a sleep cycle always exactly 90 minutes?
No. Cycles usually range from about 80 to 110 minutes and change through the night. 90 minutes is a useful average, so treat the results as a guide.
What if I wake up before my alarm?
If you wake naturally close to your alarm and feel alert, it is usually fine to get up. Consistent wake times help your body clock settle.
Is 6 hours of sleep enough?
For most adults, regularly sleeping 6 hours or less is not enough. The CDC recommends at least 7 hours a night.
What time should I go to bed if I wake up at 6 AM?
For 7.5 hours of sleep (five cycles), go to bed at about 10:15 PM, which allows 15 minutes to fall asleep. For 9 hours (six cycles), aim for about 8:45 PM.
Is it better to sleep 6 hours or 7.5 hours?
For most adults, 7.5 hours. Waking at the end of a cycle may help you feel less groggy, but total sleep matters more: the CDC recommends at least 7 hours a night for adults, and regularly sleeping 6 hours builds up sleep debt.
How accurate is a sleep calculator?
It gives an estimate based on average cycle lengths. It does not measure your own sleep, and real cycles vary from person to person and through the night. Use the results as a starting point, then adjust your bedtime over a week or two based on how you feel.
Can I use the sleep calculator for naps?
For naps, a 10 to 20 minute nap or a nap of about 90 minutes usually works best. See our guide to how long a nap should be for details.
When should I see a doctor about sleep?
See a doctor if poor sleep lasts more than a few weeks and affects your day, or if you snore loudly with pauses in breathing, which can be a sign of sleep apnoea.
Related tools
Related sleep guides
Sources
- CDC: About Sleep (recommended hours by age)
- Hirshkowitz et al. (2015), Sleep Health: National Sleep Foundation’s sleep time duration recommendations
- StatPearls (NCBI Bookshelf): Physiology, Sleep Stages
- NHLBI: Sleep Phases and Stages
- MedlinePlus: Healthy Sleep
Written by Khalid Waleed, PhD, founder and editor of Nurtavia. Read our editorial policy to see how we research and update our tools.
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