Sleep calculator
Work out when to go to bed so you wake up at the end of a sleep cycle, or when to set your alarm if you go to bed now. Add the time you usually take to fall asleep.
When should I sleep? Bedtime and wake-up calculator
Bedtimes for a 7:00 AM wake-up
- 6 cycles · 9 h of sleep · the night beforeRecommended for most adults
- 5 cycles · 7 h 30 min of sleep · the night beforeRecommended for most adults
- 4 cycles · 6 h of sleep · same dayShort night: below the 7+ hours most adults need (CDC)
- 3 cycles · 4 h 30 min of sleep · same dayShort night
Includes 15 minutes to fall asleep and 90-minute cycles. Aim for the options marked “recommended” (5–6 cycles, 7+ hours).
This calculator gives general estimates based on average 90-minute sleep cycles. It isn’t medical advice. If you have ongoing trouble sleeping, loud snoring, or daytime sleepiness, talk to a doctor.
How accurate is this? It’s an estimate. Sleep cycles average about 90 minutes, but they vary: the first cycle of the night is often 70–100 minutes and later ones 90–120 minutes [2]. That’s why you can change the cycle length and the time you take to fall asleep. Nobody can predict the exact stage you’ll be in at a given minute.
Popular wake-up times
More sleep calculators
Bedtime calculator
Four bedtimes that line up with full cycles.
Wake-up time calculator
Going to bed now or at a set time? See the best times to set your alarm.
Nap calculator
A 10–20 minute power nap or a full 90-minute cycle, with the alarm time worked out.
Sleep debt calculator
Log a week of sleep and compare it with what you need for your age.
Caffeine cutoff calculator
Estimate how much caffeine is left at bedtime and when to have your last coffee.
How much sleep by age
Recommended hours from newborns to older adults, with the source for each row.
How this sleep time calculator works
During the night you move through repeating cycles of lighter sleep, deep sleep and REM (dreaming) sleep. NIH’s National Institute of Neurological Disorders and Stroke explains that you cycle through non-REM and REM sleep several times a night, with longer REM periods later on [3]. A cycle lasts about 90 minutes on average [2].
Deep sleep (stage 3) is the stage in which it “may be difficult to awaken you” [3], and waking from deep sleep can leave you groggy [4]. The idea behind a sleep cycle calculator is simple: if your alarm goes off near the end of a cycle, you are less likely to be pulled out of deep sleep.
- Choose what you know: the time you need to wake up, or the time you’re going to bed.
- Set how long you usually take to fall asleep. Most healthy people take 15–20 minutes [1].
- Read the results. For a bedtime, the calculator subtracts that time and then 90 minutes per cycle. For a wake-up time, it adds them.
- Pick one of the options marked “recommended”: 5 or 6 cycles, which is 7.5 or 9 hours of sleep.
A worked example
Say you need to be up at 7:00 AM and you take about 15 minutes to drop off. Counting back gives these bedtimes:
| Cycles | Bedtime | Sleep |
|---|---|---|
| 6 | 9 hours | |
| 5 | 7.5 hours | |
| 4 | 6 hours | |
| 3 | 4.5 hours |
How many hours of sleep do you need?
Timing your alarm is only half the picture: the total matters more. Adults are advised to sleep 7 or more hours a night on a regular basis [5], and NHLBI says adults who sleep less than 7 hours a night may have more health issues than those who sleep 7 or more [6]. Children and teenagers need more sleep than adults; teens 13–18, for example, should get 8–10 hours [7]. Our sleep-by-age chart has every age group with its source.
When to sleep: tips for using the results
- Keep it regular. CDC lists going to bed and getting up at the same time every day as a habit that can improve sleep [8]. Pick a bedtime you can keep on most nights, including weekends.
- Lights-out counts. The bedtime is when the lights go off, not when you start getting ready.
- Watch the caffeine. A study found that caffeine taken 6 hours before bed still disrupted sleep [9]. The caffeine cutoff calculator works out your last-coffee time.
- Don’t lie awake for ages. If you can’t fall asleep within 20 to 30 minutes, the Sleep Foundation suggests getting up and doing something relaxing until you feel sleepy [1].
Want to understand the stages behind the numbers? Read sleep cycles explained, or browse the sleep FAQ.
When to talk to a doctor
A calculator can’t fix a sleep problem. CDC advises talking to your healthcare provider if you regularly have problems sleeping or notice signs of common sleep disorders such as insomnia, restless legs syndrome, narcolepsy or sleep apnea [8]. Loud snoring and feeling sleepy during the day despite enough time in bed are also worth mentioning to a doctor.
Frequently asked questions
How does a sleep calculator work?
It counts backwards (or forwards) in whole sleep cycles. For a bedtime, it takes your wake-up time, subtracts the minutes you usually need to fall asleep, then subtracts 90 minutes for each cycle. Cycles average about 90 minutes [2], so the alarm is timed for the end of a cycle rather than the middle of one.
Is a sleep calculator accurate?
It’s a rough guide, not a measurement. Real cycles vary: the first one is often 70–100 minutes and later ones 90–120 minutes [2], and they differ from night to night. Use the results as a starting point and adjust the cycle length or fall-asleep time if they don’t match how you feel.
How many hours of sleep will I get if I go to bed now?
Choose “I’m going to bed at…”, press “Sleep now” and the calculator lists wake-up times for 3 to 6 cycles, with the hours of sleep for each. Five cycles is 7.5 hours and six cycles is 9 hours at the default 90-minute cycle.
How much sleep do adults need?
The American Academy of Sleep Medicine and Sleep Research Society recommend 7 or more hours a night on a regular basis for adults [5]. CDC gives 7–9 hours for ages 61–64 and 7–8 hours from 65 [8]. Children and teens need more: see how much sleep you need by age.
Why are 5 and 6 cycles marked as recommended?
With 90-minute cycles they give 7.5 and 9 hours of sleep, which meets the “7 or more hours” adults are advised to get [5]. Four cycles is 6 hours, below that guidance, so it is marked as a short night.
How long does it take to fall asleep normally?
Most healthy people fall asleep within 15 to 20 minutes of lying down [1]. That’s why the calculator starts at 15 minutes; change it to match you.
Does the calculator store my data?
Only your settings are saved, in this browser on this device. Nothing you type is sent to us. See the privacy policy.
Is this medical advice?
No. It’s a general estimate. If you regularly have problems sleeping, talk to a healthcare provider [8]. Read the medical disclaimer.
Sources
- Sleep Foundation: How Long Should It Take to Fall Asleep?. August 21, 2025. Accessed October 21, 2026.
- Sleep Foundation: Stages of Sleep: What Happens in a Normal Sleep Cycle?. July 25, 2025. Accessed October 21, 2026.
- NINDS (NIH): Brain Basics: Understanding Sleep. February 25, 2025. Accessed October 21, 2026.
- Sleep Foundation: Napping: Benefits and Tips. May 27, 2026. Accessed October 21, 2026.
- AASM / SRS: Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the AASM and Sleep Research Society (Watson et al., J Clin Sleep Med 2015;11(6):591–592). 2015. Accessed October 21, 2026.
- NHLBI (NIH): How Much Sleep Is Enough?. March 24, 2022. Accessed October 21, 2026.
- AASM: Recommended Amount of Sleep for Pediatric Populations: A Consensus Statement of the American Academy of Sleep Medicine (Paruthi et al., J Clin Sleep Med 2016;12(6):785–786). 2016. Accessed October 21, 2026.
- CDC: About Sleep. May 15, 2024. Accessed October 21, 2026.
- PubMed: Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed (Drake et al., J Clin Sleep Med 2013;9(11):1195–1200). 2013. Accessed October 21, 2026.
Last reviewed by the CycleRest team (sources re-checked; no medical reviewer). Editorial policy