Sleep Calculator
Find when to go to bed for a wake-up time, or when to wake for a bedtime, in whole 90-minute sleep cycles, with recommended sleep hours by age.
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Sleep Calculator
To wake up at 6:30 AM, go to bed at…
- 9:15 PMRecommended
6 cycles · 9 h asleep · the night before
Within the recommended range for your age group
- 10:45 PMRecommended
5 cycles · 7 h 30 min asleep · the night before
Within the recommended range for your age group
- 12:15 AM
4 cycles · 6 h asleep
Outside the recommended range for your age group
- 1:45 AM
3 cycles · 4 h 30 min asleep
Outside the recommended range for your age group
Times are when to be in bed: each one allows 15 minutes to fall asleep, then whole 90-minute cycles. The recommended range for ages 26–64 years is 7–9 h a day. Cycle lengths vary from person to person and through the night, so treat these as starting points and adjust to how you feel.
Recommended sleep by age
| Age group | Ages | NSF | AASM |
|---|---|---|---|
| Newborn | 0–3 months | 14–17 h | — |
| Infant | 4–11 months | 12–15 h | 12–16 h |
| Toddler | 1–2 years | 11–14 h | 11–14 h |
| Preschool | 3–5 years | 10–13 h | 10–13 h |
| School age | 6–13 years | 9–11 h | 9–12 h |
| Teen | 14–17 years | 8–10 h | 8–10 h |
| Young adult | 18–25 years | 7–9 h | 7+ h |
| Adult | 26–64 years | 7–9 h | 7+ h |
| Older adult | 65+ years | 7–8 h | — |
Hours per 24 hours, including naps for babies and young children. NSF: National Sleep Foundation (2015). AASM: American Academy of Sleep Medicine — its pediatric consensus (2016) uses slightly different age bands (4–12 months, 6–12 and 13–18 years), and its adult guidance (with the Sleep Research Society, 2015) is at least 7 hours for ages 18–60. General guidance, not medical advice.
About Sleep Calculator
Sleep isn't one long stretch: through the night you move through repeating cycles of light sleep, deep sleep, and REM sleep, each lasting roughly an hour and a half. Waking at the end of a cycle, when sleep is lightest, tends to feel easier than being pulled out of deep sleep partway through one. This calculator lines your alarm or your bedtime up with those cycle boundaries.
Choose I want to wake up at and enter your alarm time to get bedtimes that fit six, five, four, or three whole cycles before it. Choose I'm going to bed at — or press Going to bed now — to get the wake-up times that land on a cycle boundary. Both directions allow 15 minutes to fall asleep first, and both handle midnight properly: a 10:45 PM bedtime for a 6:30 AM alarm is marked as the night before.
Five or six cycles (7½ to 9 hours of sleep) is highlighted as the target for most adults, matching the 7–9 hours sleep organisations recommend. Pick your age group to see the recommended range for it and whether each option falls inside it; the table under the calculator lists the ranges for every age.
Adjusting the assumptions
Both numbers the calculation rests on are in Options:
- Time to fall asleep — 15 minutes by default. Most healthy adults take 10–20 minutes; if you're usually out in five, or lie awake for half an hour, change it.
- Sleep cycle length — 90 minutes by default. That's the textbook average, but real cycles vary from about 70 to 120 minutes between people, and the same person's cycles change through the night (more deep sleep early, longer REM periods toward morning). If you regularly wake just before your alarm, that's a hint about your own rhythm.
Example
Input
Wake up at 6:30 AM
Output
9:15 PM (6 cycles, 9 h) 10:45 PM (5 cycles, 7 h 30 min) 12:15 AM (4 cycles, 6 h) 1:45 AM (3 cycles, 4 h 30 min)
Each bedtime is the 6:30 alarm minus the cycles and 15 minutes to fall asleep. If 10:45 PM is too early, 12:15 AM ends on a cycle boundary too — but six hours is short of what most adults need, so it's a fallback rather than a plan.
Limitations
- The 90-minute cycle is an average, not a clock inside you. Treat the suggested times as starting points and adjust to how you actually feel.
- Total sleep matters more than timing. Waking between cycles after five hours won't make up for a short night.
- Recommendations are general guidance for healthy people. Persistent trouble sleeping, loud snoring, or daytime sleepiness despite enough time in bed are worth raising with a doctor — this tool isn't medical advice.
Frequently asked questions
What time should I go to bed if I wake up at 6:30?
For five 90-minute cycles plus 15 minutes to fall asleep, be in bed by 10:45 PM; for six cycles, 9:15 PM. Those give 7½ and 9 hours of sleep. If you take longer to fall asleep, move the bedtime earlier by the difference.
How long is a sleep cycle?
About 90 minutes on average, but it ranges from roughly 70 to 120 minutes and changes through the night: early cycles carry more deep (slow-wave) sleep, and later ones longer REM periods. A typical night has four to six cycles.
Is it better to wake up at the end of a sleep cycle?
Waking from light sleep at the end of a cycle usually feels easier than waking from deep sleep, which can leave you groggy for a while (sleep inertia). That's the idea behind cycle-based bedtimes. Because cycle length varies, though, the timing is an estimate — getting enough total sleep matters more.
How much sleep do adults need?
The National Sleep Foundation recommends 7–9 hours for adults 18–64 and 7–8 hours for those 65 and older. The American Academy of Sleep Medicine and Sleep Research Society recommend at least 7 hours a night for adults 18–60. Teens need 8–10 hours and school-age children 9–11 (NSF) or 9–12 (AASM).
How much sleep do babies and children need?
Including naps: newborns 14–17 hours, infants 12–15 (NSF) or 12–16 (AASM), toddlers 11–14, preschoolers 10–13, and school-age children 9–11 or 9–12. Babies' sleep cycles are shorter than adults', so cycle-based bedtimes don't apply to them — use the hours as a guide instead.
How long does it take to fall asleep?
Most healthy adults fall asleep within 10 to 20 minutes of lying down, which is why the calculator assumes 15. Falling asleep in under five minutes can be a sign of sleep debt; regularly taking more than 30 is worth mentioning to a doctor.
Does it handle bedtimes after midnight?
Yes. Times wrap around midnight correctly and are labelled: a bedtime before a morning alarm shows as the night before when it falls in the evening, and wake-up times after a late bedtime show as the next day.
Is my information stored?
No. The calculator runs in your browser and doesn't save or send the times you enter. "Going to bed now" reads the clock on your own device.