Sleep Calculator

Sleep Calculator

Choose when you want to wake up — or when you’re going to bed — and get times that fit whole sleep cycles, allowing for the time it takes to fall asleep.

I want to wake up at… I’m going to bed at…

Wake-up time

Time to fall asleep

min

15 is typical

Sleep cycle length

min

About 90 on average

Recommend for CDC hours of sleep by age

12-hour 24-hour

Example Set your own time above.

To wake up at 7:00 AM, go to bed at:

9:45 PM6 cycles · 9 h of sleepRecommended
11:15 PM5 cycles · 7 h 30 min of sleepRecommended
12:45 AM4 cycles · 6 h of sleep
2:15 AM3 cycles · 4 h 30 min of sleep

Bedtimes include 15 minutes to fall asleep. Recommended = within the 7 or more hours of sleep the CDC advises for adults aged 18–60.

Working

Assumed: 90-minute sleep cycles and 15 minutes to fall asleep.
6 cycles: 6 × 90 min = 540 min (9 h). 7:00 AM − 9 h = 10:00 PM asleep; − 15 min to fall asleep = 9:45 PM bedtime
5 cycles: 5 × 90 min = 450 min (7 h 30 min). 7:00 AM − 7 h 30 min = 11:30 PM asleep; − 15 min to fall asleep = 11:15 PM bedtime
4 cycles: 4 × 90 min = 360 min (6 h). 7:00 AM − 6 h = 1:00 AM asleep; − 15 min to fall asleep = 12:45 AM bedtime
3 cycles: 3 × 90 min = 270 min (4 h 30 min). 7:00 AM − 4 h 30 min = 2:30 AM asleep; − 15 min to fall asleep = 2:15 AM bedtime
The CDC recommends 7 or more hours of sleep for adults aged 18–60, so 6 cycles (9 h) and 5 cycles (7 h 30 min) qualify.

How to use the sleep calculator

Choose I want to wake up at… and enter your alarm time to see bedtimes that fit three to six complete sleep cycles, or choose I’m going to bed at… (or press Going to bed now) to see when to set the alarm. Times marked Recommended give you the amount of sleep the CDC recommends for the age group you pick. If you usually take longer than 15 minutes to drop off, or you know your cycles run shorter or longer than 90 minutes, change those settings — every time updates instantly and the working shows how each one was found. Your settings are kept in the page address, so you can bookmark them.

How the times are calculated

bedtime      = wake-up time − (cycles × cycle length) − time to fall asleep
wake-up time = bedtime + time to fall asleep + (cycles × cycle length)

The idea is to wake up near the end of a cycle, when sleep is lighter, instead of in the middle of deep sleep. The calculator counts whole cycles only and shows 3 to 6 of them: 4½, 6, 7½ and 9 hours of sleep at 90 minutes each.

Worked example

You need to be up at 7:00 AM. Five cycles of 90 minutes is 450 minutes, or 7 hours 30 minutes, so you should be asleep by 11:30 PM; allowing 15 minutes to fall asleep, go to bed at 11:15 PM. Six cycles (9 hours) means bed at 9:45 PM. Four cycles gives a 12:45 AM bedtime and three cycles 2:15 AM — but that is only 6 or 4½ hours of sleep, below the 7 hours or more recommended for adults, so only the first two are marked Recommended.

How much sleep do you need?

The CDC’s recommended hours of sleep by age:

Age group	Age	Recommended sleep
Newborn	0–3 months	14–17 hours (National Sleep Foundation; the AASM makes no recommendation)
Infant	4–12 months	12–16 hours per 24 hours, including naps
Toddler	1–2 years	11–14 hours per 24 hours, including naps
Preschool	3–5 years	10–13 hours per 24 hours, including naps
School age	6–12 years	9–12 hours per 24 hours
Teen	13–17 years	8–10 hours per 24 hours
Adult	18–60 years	7 or more hours per night
Adult	61–64 years	7–9 hours
Adult	65 years and older	7–8 hours

The CDC’s figures come from consensus statements by the American Academy of Sleep Medicine (AASM) — whose pediatric statement covers teens up to 18 — and from the National Sleep Foundation. The AASM and Sleep Research Society add that regularly sleeping more than 9 hours may be appropriate for young adults, people recovering from sleep debt and people who are ill. Babies’ and young children’s sleep doesn’t follow adult 90-minute cycles, so this calculator is meant for teens and adults.

Sleep cycles: what’s solid and what’s not

Cycles are real. Through the night you move through the stages of non-REM sleep (from light N1 and N2 to deep N3) and then REM sleep, several times over. REM sleep first arrives about 90 minutes after falling asleep; early cycles contain more deep sleep and later ones more REM.
90 minutes is an average, not a rule. NINDS puts a full cycle at roughly 90 to 110 minutes and StatPearls at about 90 minutes on average, with four to six cycles a night. Your own cycles differ from those averages and from each other, so the times here are estimates, not precise alarms. If 90 minutes doesn’t suit you, try 80 or 100.
Falling asleep takes time. The National Sleep Foundation treats falling asleep within 15 minutes as a sign of good sleep quality, so 15 minutes is the default. The bedtime shown is when to turn the lights out, not when you will be asleep.
Total sleep matters most. Waking from deep sleep can cause a short spell of grogginess called sleep inertia, but consistently getting enough sleep matters far more than hitting the end of a cycle. Pick a Recommended time and keep the same wake-up time every day, weekends included.

This calculator is general information, not medical advice. Persistent trouble sleeping, loud snoring or daytime sleepiness is worth raising with a doctor. To count down to bedtime, try the countdown timer; to add up hours of sleep over several nights, the time calculator.

Frequently asked questions

What time should I go to bed if I wake up at 6 AM?

With 90-minute cycles and 15 minutes to fall asleep, aim for 8:45 PM (six cycles, 9 hours of sleep) or 10:15 PM (five cycles, 7½ hours). Both give an adult the 7 or more hours recommended. 11:45 PM (four cycles) is only 6 hours of sleep — fine once in a while, but not enough as a habit.

How long is a sleep cycle?

About 90 minutes on average. NINDS puts a complete cycle at roughly 90 to 110 minutes, and StatPearls describes four to six cycles in a night. The length varies between people and through the night — early cycles contain more deep sleep, later ones more REM sleep — so the times here are estimates. You can change the cycle length in the calculator.

How much sleep do adults need?

The American Academy of Sleep Medicine and the Sleep Research Society recommend 7 or more hours a night for adults, and the CDC uses the same figure for ages 18–60. For ages 61–64 the CDC lists 7–9 hours, and for 65 and older 7–8 hours. Teens aged 13–17 need 8–10 hours.

Is it better to sleep 6 hours or 7½ hours?

Seven and a half. Waking at the end of a cycle may feel easier than being woken from deep sleep, but the total amount of sleep matters far more: sleeping 6 hours or less a night is below what adults need for health and safety according to the AASM and Sleep Research Society. Choose the latest bedtime that still gives you at least five cycles.

How long should it take to fall asleep?

For most people, about 15 minutes or less. The National Sleep Foundation’s sleep-quality recommendations treat falling asleep within 15 minutes as a sign of good sleep quality at every age, which is why this calculator allows 15 minutes by default. If it regularly takes you much longer, change the setting — and consider mentioning it to a doctor.

Why do I wake up tired even after 8 hours in bed?

Time in bed is not the same as sleep: long wake-ups during the night, an irregular schedule, alcohol or caffeine late in the day, or a sleep disorder such as sleep apnea can all leave you tired. Waking from deep sleep can also cause temporary grogginess (sleep inertia). If tiredness persists, snoring is loud or you stop breathing in your sleep, talk to a doctor — these problems are common and treatable.

Last reviewed 25 September 2026 · Built and checked by the Reeliy team · How we test our tools