Sleep Calculator
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Results
To wake up at 7:00 AM, go to bed at 11:15 PM (5 sleep cycles, 7 h 30 min of sleep)
| Cycles | Sleep | Go to bed at | Ages 18–60 years: 7 or more hours |
|---|---|---|---|
| 6 | 9 h | 9:45 PM | Within the range |
| 5 | 7 h 30 min | 11:15 PM | Within the range |
| 4 | 6 h | 12:45 AM | Less than recommended |
| 3 | 4 h 30 min | 2:15 AM | Less than recommended |
Times assume 1 h 30 min cycles and 15 min to fall asleep. Sleep cycles are a rule of thumb: getting enough hours matters more than hitting the end of a cycle.
This is a rule-of-thumb estimate, not medical advice. If you often struggle to fall or stay asleep, snore loudly, or feel very sleepy during the day, talk to a doctor.
How to use the sleep calculator
- Choose what you want to know: a bedtime for a set wake-up time, a wake-up time for a set bedtime, or a wake-up time if you go to bed now.
- Enter the time. "Go to bed now" uses the clock on your device, and the button under the form switches to it at any time.
- Pick your age group, then adjust the cycle length and the time it usually takes you to fall asleep if the defaults (90 and 15 minutes) don't suit you.
- Read the suggested time, then compare the other options in the table with the recommended hours for your age.
Sleep cycle formula
wake-up time = bedtime + time to fall asleep + (cycles × cycle length)
During the night you move through repeating cycles of lighter non-REM sleep, deep sleep and REM (dreaming) sleep. The cycles average roughly 90 minutes, but they vary from person to person and from one cycle to the next, with longer REM periods toward morning. The idea behind this calculator is a rule of thumb: an alarm that goes off near the end of a cycle, when sleep is lighter, may feel easier than one that wakes you from deep sleep. The "time to fall asleep" covers the minutes between lights out and actually sleeping; the calculator uses 15 minutes unless you change it.
The cycles are the "how", not the "how much". The hours themselves come from expert consensus statements, and they matter more than landing exactly on a cycle boundary.
Worked example
You need to be up at 7:00 AM. Six 90-minute cycles are 9 h of sleep; add 15 minutes to fall asleep and you should be in bed by 9:45 PM. Five cycles (7 h 30 min) give a bedtime of 11:15 PM, and four cycles (6 h) give 12:45 AM. For an adult aged 18 to 60, who needs 7 or more hours, the shortest option that reaches the minimum is 5 cycles, so the calculator suggests 11:15 PM; four cycles fall short. A teenager, who needs 8–10 hours, would be pointed to 6 cycles instead.
Going the other way, if you go to bed at 11:00 PM, five cycles after 15 minutes of drifting off take you to 6:45 AM.
Bedtimes for common wake-up times
With 90-minute cycles and 15 minutes to fall asleep:
| Wake up at | 6 cycles (9 h) | 5 cycles (7 h 30 min) | 4 cycles (6 h) |
|---|---|---|---|
| 5:30 AM | 8:15 PM | 9:45 PM | 11:15 PM |
| 6:00 AM | 8:45 PM | 10:15 PM | 11:45 PM |
| 6:30 AM | 9:15 PM | 10:45 PM | 12:15 AM |
| 7:00 AM | 9:45 PM | 11:15 PM | 12:45 AM |
| 7:30 AM | 10:15 PM | 11:45 PM | 1:15 AM |
| 8:00 AM | 10:45 PM | 12:15 AM | 1:45 AM |
How much sleep do you need?
The CDC lists these amounts per 24 hours, taken from consensus statements by the American Academy of Sleep Medicine (AASM), the Sleep Research Society (SRS) and the National Sleep Foundation. For babies and young children the hours include naps.
| Age group | Age | Recommended sleep | Source |
|---|---|---|---|
| Newborn | 0–3 months | 14–17 hours | National Sleep Foundation (Hirshkowitz et al., 2015) |
| Infant | 4–12 months | 12–16 hours (including naps) | AASM (Paruthi et al., 2016) |
| Toddler | 1–2 years | 11–14 hours (including naps) | AASM (Paruthi et al., 2016) |
| Preschool | 3–5 years | 10–13 hours (including naps) | AASM (Paruthi et al., 2016) |
| School age | 6–12 years | 9–12 hours | AASM (Paruthi et al., 2016) |
| Teen | 13–17 years | 8–10 hours | AASM (Paruthi et al., 2016) |
| Adult | 18–60 years | 7 or more hours | AASM and SRS (Watson et al., 2015) |
| Adult | 61–64 years | 7–9 hours | National Sleep Foundation (Hirshkowitz et al., 2015) |
| Adult | 65 years and older | 7–8 hours | National Sleep Foundation (Hirshkowitz et al., 2015) |
The calculator offers the age groups from 6 years up. Babies and toddlers sleep in shorter cycles and nap during the day, so a 90-minute bedtime count doesn't describe their sleep well.
Tips for using your result
- Hours first, cycles second. If the only bedtime that lands on a cycle boundary leaves you short of your recommended hours, go to bed earlier rather than cutting a cycle.
- Keep it regular. A similar bedtime and wake-up time every day, weekends included, makes the schedule easier to keep.
- Tune the inputs. If you regularly wake just before the alarm, or feel groggy at a suggested time, try a cycle length a little shorter or longer than 90 minutes.
- Be honest about falling asleep. If it usually takes you 30 minutes, enter 30; the bedtime moves earlier by the same amount.
Shift workers can use the same method with any clock time: enter the time you need to be up, even if it is in the afternoon. To plan a whole day, the time duration calculator counts the hours between two times, and the calorie calculator estimates daily energy needs.
Persistent trouble sleeping, loud snoring, pauses in breathing or heavy daytime sleepiness can be signs of a sleep disorder that needs proper assessment. This is not medical advice; talk to a doctor about your own sleep.
Sources
- CDC, About Sleep (May 15, 2024): recommended hours of sleep by age.
- Paruthi S et al., Recommended amount of sleep for pediatric populations: a consensus statement of the American Academy of Sleep Medicine, J Clin Sleep Med 2016;12(6):785–786.
- Watson NF et al., Recommended amount of sleep for a healthy adult: a joint consensus statement of the AASM and Sleep Research Society, Sleep 2015;38(6):843–844.
- Hirshkowitz M et al., National Sleep Foundation's sleep time duration recommendations, Sleep Health 2015;1(1):40–43.
- National Institute of Neurological Disorders and Stroke, Brain Basics: Understanding Sleep: sleep stages and cycles.
Frequently asked questions
What time should I go to bed to wake up at 7 AM?
With 90-minute sleep cycles and 15 minutes to fall asleep, go to bed at 11:15 PM for five cycles (7 hours 30 minutes of sleep) or 9:45 PM for six cycles (9 hours). Adults aged 18 to 60 need 7 or more hours, so 12:45 AM (four cycles, 6 hours) is too late.
How long is a sleep cycle?
About 90 minutes on average, but it is a rule of thumb rather than a fixed number: cycles differ between people and change through the night, with longer REM periods toward morning. You can set the cycle length in the calculator; with 100-minute cycles, five cycles are 8 hours 20 minutes.
How many hours of sleep do I need?
The CDC, drawing on AASM and National Sleep Foundation consensus statements, lists 9 to 12 hours for ages 6 to 12, 8 to 10 hours for teens aged 13 to 17, 7 or more hours for adults aged 18 to 60, 7 to 9 hours for ages 61 to 64 and 7 to 8 hours from 65.
What if I go to bed now?
Choose "Go to bed now" or press the button under the form. The calculator reads the time on your device, adds the time it takes you to fall asleep and counts whole cycles forward. Going to bed at 11:00 PM gives a 6:45 AM wake-up for five cycles.
Is waking at the end of a sleep cycle proven to feel better?
It is a popular rule of thumb, not a guarantee. Lighter sleep near the end of a cycle may make waking easier, but cycle lengths vary, so the times are estimates. Getting enough total sleep matters more. If you often feel unrefreshed or very sleepy in the day, talk to a doctor.