Find a bedtime or wake-up time that lines up with your sleep cycles — and change the numbers to match how you actually sleep.
Most healthy adults take roughly 10–20 minutes. Set it to your own.
90 minutes is an adult average, not a rule. Yours can be shorter or longer.
Sleep comes in cycles. For adults a cycle is commonly cited as averaging about 90 minutes, and many people find waking at the end of one easier than being woken part-way through. This calculator counts back (or forward) in whole cycles from the time you give it, and adds the time it takes you to fall asleep.
Treat the times as a starting point. Cycle length varies from person to person and from night to night, and cycles are not all the same length within a single night. That’s why the cycle length and fall-asleep time are adjustable. If you consistently wake up groggy, try shifting your cycle length by 5–10 minutes for a week and see what feels better.
For children the picture is different: young children’s sleep cycles are shorter than adults’ and settle toward the adult pattern as they grow. So for kids and teens we use recommended hours of sleep by age instead of counting adult-length cycles.
The only way to measure your sleep cycles properly is a sleep study that records brain activity, which is done in a lab. Short of that, these options can help you work out your own time to fall asleep and the wake-up times that suit you, roughly from most to least accessible.
| Option | What it can tell you | Limits |
|---|---|---|
| Sleep diary (free) | Your usual bedtime, how long you take to fall asleep, night wake-ups and how you feel on waking, tracked over one to two weeks. | Relies on your own estimate. People often misjudge when they fell asleep. |
| Smartwatch, band or ring | Total sleep and sleep/wake patterns over time, plus a rough time-to-fall-asleep estimate. | Estimates sleep from movement and heart rate. Tends to count quiet wakefulness as sleep, and is weak at sleep stages and cycle length. |
| Under-mattress or bedside sensor | Movement, breathing and heart rate without wearing anything. | Similar limits to wearables. Better for trends than single nights. |
| Phone sleep app | Broad patterns such as restless nights or snoring, using sound and movement. | Usually the least accurate option. |
| Consumer EEG headband | Brain-activity based, so closer to a lab than a watch. | Less comfortable and more expensive. Check how a specific product has been validated. |
| Doctor-arranged tests | Actigraphy (a medical-grade wrist device worn for a week or two) or a home sleep test, mainly used to check for sleep apnea. | Needs a doctor’s referral. A sign to get help if you have ongoing sleep problems, not a do-it-yourself tool. |
General information only. Accuracy varies by device and by person, so treat any tracker’s numbers as estimates.
| Age | Recommended sleep per 24 hours |
|---|---|
| 1–2 years | 11–14 hours, including naps |
| 3–5 years | 10–13 hours, including naps |
| 6–12 years | 9–12 hours |
| 13–18 years | 8–10 hours |
| Adults (18–60) | 7 or more hours (individual needs vary) |
Sources: American Academy of Sleep Medicine pediatric consensus statement (2016); AASM and Sleep Research Society adult consensus statement (2015), which covers adults aged 18–60. Babies under 12 months need more sleep and a different approach, so this tool isn’t designed for infants.
What time should I go to bed?
It depends on when you need to get up. Choose “I need to wake up at…”, enter your wake-up time, and the calculator counts back in whole sleep cycles and adds the time it takes you to fall asleep. Adults are advised to get 7 or more hours, so the 5- and 6-cycle bedtimes (7½ and 9 hours at 90 minutes per cycle) are the ones to aim for when you can.
Is this a bedtime calculator or a wake-up time calculator?
Both. “I need to wake up at…” works as a bedtime calculator: give it a wake-up time and it suggests when to be in bed. “I’m going to bed at…” works as a wake-up time calculator: give it your bedtime and it suggests when to wake up.
How does a sleep cycle calculator work?
Sleep moves through repeating cycles, commonly cited as averaging about 90 minutes in adults. The calculator takes 3 to 6 whole cycles, adds the time you take to fall asleep, and counts back from your wake-up time (or forward from your bedtime). Because cycle length varies between people, you can change it under “Fine-tune for how you sleep”.
Why are the suggested times a bit odd, like 10:45 PM?
They’re counted in whole cycles plus your fall-asleep time. If you can’t hit one exactly, being a few minutes either side is normal — it’s an estimate, not a deadline.
Is 90 minutes the right cycle length for me?
Not necessarily. 90 minutes is a commonly cited adult average, but cycle length varies between people and from night to night, and figures of roughly 70–120 minutes are often quoted. If you consistently wake up groggy, you could try changing the cycle length by 5–10 minutes for a week and see how you feel. Only a lab study that records brain activity can measure your own cycle length properly.
Can my smartwatch tell me my cycle length?
Not reliably. Watches estimate sleep from movement and heart rate, which works reasonably well for total sleep but poorly for sleep stages, and cycle length depends on getting the stages right. Their time-to-fall-asleep estimate is a reasonable starting point, but treat it as a guess.
How long should a nap be?
A nap of around 20 minutes is the common suggestion, because it usually ends before deep sleep and makes waking easier. A full cycle (about 90 minutes for many adults) lets you wake at the end of a cycle, but it takes longer and can make it harder to fall asleep that night. The nap tab shows both.
How much sleep do I need?
It depends on your age. The American Academy of Sleep Medicine recommends 11–14 hours (including naps) for ages 1–2, 10–13 hours (including naps) for ages 3–5, 9–12 hours for ages 6–12 and 8–10 hours for ages 13–18. For adults, the AASM and the Sleep Research Society recommend 7 or more hours on a regular basis. Individual needs vary.
Does the calculator work for shift workers?
The maths is the same — use the wake-up time or bedtime that fits your shift. People often find daytime sleep harder, so you may want to allow a longer fall-asleep time.
When should I see a doctor?
If you regularly can’t fall asleep, wake often, snore heavily, or feel exhausted despite enough hours, speak to a doctor. A calculator can’t diagnose a sleep problem.
General information only, not medical advice. Sleep needs vary between people. Sources: American Academy of Sleep Medicine and Sleep Research Society (recommended hours of sleep); Sleep Foundation (typical time to fall asleep). If you have ongoing trouble sleeping, see a doctor.
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