To wake up at 7:00 AM, get into bed at 11:15 PM the night before
An adult sleep cycle averages about 90 minutes, so counting back from your wake-up time in 90-minute steps gives bedtimes that end a cycle at the moment you wake. If you wake at 7:00 AM and need 15 minutes to fall asleep, getting into bed at 11:15 PM the night before gives you 5 cycles (7 hours 30 minutes), which also meets the adult recommendation of 7 hours or more.
Changing the number of cycles shifts the time: 9 hours (6 cycles) means 9:45 PM, and 6 hours (4 cycles) means 12:45 AM. Below you will find how the calculation works, tables by wake-up time and bedtime, what a sleep cycle is, and the recommended sleep by age group.
How it is calculated
- Find bedtime: wake-up time - time to fall asleep - 90 minutes x number of cycles = time to get into bed.
- Find wake time: bedtime + time to fall asleep + 90 minutes x number of cycles = wake-up time. "Sleep now" uses the current time as your bedtime.
- Total sleep = 90 minutes x number of cycles. The time to fall asleep is added to the time in bed only, not to the sleep time.
- Check the recommendation: the result is compared with the recommended sleep for the chosen age group and marked as in range, short, or long. The shortest option that meets the recommendation is shown in large type.
Bedtime for each wake-up time
| Wake-up time | 4 cycles (6 h) | 5 cycles (7 h 30 min) | 6 cycles (9 h) |
|---|---|---|---|
| 5:30 AM | 11:15 PM | 9:45 PM | 8:15 PM |
| 6:00 AM | 11:45 PM | 10:15 PM | 8:45 PM |
| 6:30 AM | 12:15 AM | 10:45 PM | 9:15 PM |
| 7:00 AM | 12:45 AM | 11:15 PM | 9:45 PM |
| 7:30 AM | 1:15 AM | 11:45 PM | 10:15 PM |
| 8:00 AM | 1:45 AM | 12:15 AM | 10:45 PM |
Values assume 15 minutes to fall asleep. For adults, 5 cycles is the first option that meets the recommendation of 7 hours or more. Bedtimes before midnight fall on the day before you wake up.
Wake-up time for each bedtime
| Bedtime | 4 cycles (6 h) | 5 cycles (7 h 30 min) | 6 cycles (9 h) |
|---|---|---|---|
| 9:30 PM | 3:45 AM | 5:15 AM | 6:45 AM |
| 10:00 PM | 4:15 AM | 5:45 AM | 7:15 AM |
| 10:30 PM | 4:45 AM | 6:15 AM | 7:45 AM |
| 11:00 PM | 5:15 AM | 6:45 AM | 8:15 AM |
| 11:30 PM | 5:45 AM | 7:15 AM | 8:45 AM |
| 12:00 AM | 6:15 AM | 7:45 AM | 9:15 AM |
| 12:30 AM | 6:45 AM | 8:15 AM | 9:45 AM |
If you get into bed at 11:00 PM, wake up at 6:45 AM after 5 cycles or at 8:15 AM after 6 cycles.
What a sleep cycle is
Sleep repeats in units made of non-REM sleep, which goes from light to deep sleep, and REM sleep, in which most dreaming occurs. In adults one unit lasts about 90 minutes on average and repeats 4 to 6 times a night. The length varies by person and by night, so use the calculated times as a rough guide to a good moment to wake.
In healthy adults, falling asleep after lying down is generally reported to take 10 to 20 minutes, and frequently taking more than 30 minutes can be a sign of insomnia. You can enter this time yourself, and the calculator uses 15 minutes when it is left blank.
Recommended sleep by age group
| Age group | Recommended sleep | In 90-minute cycles | Source |
|---|---|---|---|
| Ages 6-12 | 9-12 hours | 6-7 cycles | AASM 2016 |
| Ages 13-18 | 8-10 hours | 6 cycles | AASM 2016 |
| Adults (ages 18-60) | 7 hours or more | 5 cycles or more | AASM and SRS 2015 |
| Ages 65+ | 7-8 hours | 5 cycles | NSF 2015 |
Japan's Ministry of Health, Labour and Welfare Sleep Guide 2023 advises adults to sleep at least 6 hours, and advises older people to keep their time in bed to within 8 hours. A Korea Disease Control and Prevention Agency (KDCA) release from April 2026 on the 2025 Community Health Survey found that people sleeping 6 hours or less or 9 hours or more had 2.1 times the odds of depressive symptoms of those sleeping 7 to 8 hours, and the agency cautions against reading this as cause and effect.
Common mistakes
- Forgetting the time to fall asleep: for a 7:00 AM wake-up with 5 cycles, the answer is 11:15 PM, not 11:30 PM, because the 15 minutes to fall asleep must be subtracted too.
- Matching cycles but ignoring total sleep: 4 cycles (6 hours) fits the cycle count but falls short of the adult recommendation of 7 hours.
- Treating cycle times as exact: 90 minutes is an average, and your actual cycles can be shorter or longer.
Limits and cautions
- The cycle length is fixed at 90 minutes. Real cycles and the time to fall asleep vary by person and night, so results are estimates.
- The recommendation refers to total sleep over a day, and for children it can include naps.
- Nights when the clock changes for daylight saving time are not accounted for.
- If you struggle to fall asleep, or stay sleepy during the day even after enough sleep, talk to a health professional.
Last checked The recommended sleep times and the description of sleep cycles in this article were checked on 2026-10-08 against society consensus statements, journal articles and the original pages of each organization.
Sources
- 01Watson NF, et al. Recommended Amount of Sleep for a Healthy Adult (AASM and SRS). J Clin Sleep Med 2015"Adults should sleep 7 or more hours per night on a regular basis", ages 18-60
- 02Paruthi S, et al. Recommended Amount of Sleep for Pediatric Populations (AASM). J Clin Sleep Med 2016Ages 6-12: 9-12 hours; ages 13-18: 8-10 hours (per 24 hours)
- 03Hirshkowitz M, et al. National Sleep Foundation's sleep time duration recommendations. Sleep Health 2015Adults 7-9 hours, older adults 7-8 hours
- 04StatPearls: Physiology, Sleep StagesAll stages cycle about 4-6 times a night, with an average cycle of 90 minutes
- 05PMC5390528 reviewNon-REM and REM sleep alternate about every 90 minutes, 4-5 times a night
- 06PMC12282543 studyNormal sleep onset latency is generally 10-20 minutes, and more than 30 minutes suggests insomnia
- 07Japan Ministry of Health, Labour and Welfare: Sleep Guide for Health 2023 (健康づくりのための睡眠ガイド2023)Adults at least 6 hours, older people within 8 hours in bed, durations for children by age
- 08Korea Disease Control and Prevention Agency press release (2025 Community Health Survey, 2026-04-14)Odds ratio of 2.1 for depressive symptoms at 6 hours or less or 9 hours or more of sleep compared with 7-8 hours; not a causal finding
Frequently asked questions
How does the sleep calculator work?
It counts back from your wake-up time by the time it takes to fall asleep and by as many 90-minute cycles as you choose. If you wake at 7:00 AM and need 15 minutes to fall asleep, 5 cycles (7 h 30 min) means going to bed at 11:15 PM the night before, and 6 cycles (9 h) means 9:45 PM. If you enter a bedtime, it adds forward instead.
Why is a sleep cycle 90 minutes?
Sleep repeats a set of light and deep non-REM sleep followed by REM sleep. In adults one set averages about 90 minutes and repeats 4 to 6 times a night. The length varies between people and nights, so treat the results as estimates.
How many hours should adults sleep?
The American Academy of Sleep Medicine and the Sleep Research Society recommend 7 or more hours per night for adults aged 18 to 60. With 90-minute cycles, 5 cycles (7 h 30 min) is the first option that meets this. Japan's Ministry of Health, Labour and Welfare 2023 sleep guide recommends at least 6 hours for adults.
How many hours should children and teens sleep?
The AASM 2016 consensus recommends 9 to 12 hours a day for ages 6 to 12 and 8 to 10 hours for ages 13 to 18. With 90-minute cycles, ages 6 to 12 fall in range with 6 or 7 cycles (9 h to 10 h 30 min) and ages 13 to 18 with 6 cycles (9 h).
What should I enter as the time to fall asleep?
Enter how long it usually takes you to fall asleep after lying down. Healthy adults are reported to take about 10 to 20 minutes, and the calculator uses 15 minutes if you leave it blank. Often taking more than 30 minutes can be a sign of insomnia.
What does Sleep now do?
It treats the current time as your bedtime and adds the time to fall asleep and 90-minute cycles to show when to wake up. It uses your device clock and recalculates when the minute changes while the page is open.
How many hours should people 65 and older sleep?
The National Sleep Foundation's 2015 recommendation is 7 to 8 hours for people 65 and older. With 90-minute cycles, 5 cycles (7 h 30 min) falls in this range. Japan's guide advises older adults not to spend more than 8 hours in bed.
Will I always feel refreshed if I wake at the end of a cycle?
That cannot be guaranteed. Cycle length is an average that varies between people and nights, and feeling refreshed also depends on total sleep and sleep quality. The calculator shows both cycle-aligned times and whether you meet the recommended sleep, so look at both.