Find when to go to bed or wake up so you finish a complete sleep cycle, or pick a sleep length and get a single bedtime or alarm. Times wrap past midnight and, in the cycle tab, include the minutes you take to fall asleep.
Formula
Sleep-cycle times count whole cycles on a 24-hour clock (1,440 minutes). The active target is a wake time or a bedtime:
bedtime = wakeTime − fallAsleep − n × cycleLength
wakeTime = bedtime + fallAsleep + n × cycleLength
n runs from 1 to 7. Results are shown in the order 5, 6 (recommended), then 7, 4, 3, 2, 1, each wrapped with mod 1,440. Defaults are a 90-minute cycle and 15 minutes to fall asleep.
Sleep length is the same clock arithmetic without cycles:
bedtime = wakeTime − duration
wakeTime = bedtime + duration
Cycle length is an average, not a stopwatch. Adult cycles often run 80–110 minutes and get longer toward morning. Treat the highlighted 5- and 6-cycle times as targets, not exact alarms.
How much sleep by age
CDC-recommended hours of sleep per 24 hours (naps included where noted):
| Age group | Recommended sleep |
|---|---|
| 0–3 months | 14–17 hours |
| 4–12 months | 12–16 hours (including naps) |
| 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 |
| 18–60 years | 7 or more hours per night |
| 61–64 years | 7–9 hours |
| 65 years and older | 7–8 hours |
Sleep cycles, REM, and quality
A cycle is the swing from non-REM sleep (including deep, slow-wave sleep) into REM sleep, when most dreaming happens. The brain uses less energy in non-REM and restores ATP; growth hormone is secreted in slow-wave sleep. REM is a smaller share of the night. Waking in the middle of a cycle — especially deep sleep — is what makes alarms feel brutal; landing at the end of a cycle is the point of the times above.
Sleep timing also follows the circadian clock. Jet lag is that clock still running on the old local time. Light, work hours, naps, and genetics all shift when you actually fall asleep. Sleep quality is how easily you fall and stay asleep, how often you wake, and how rested you feel — not only hours in bed.
Examples
Wake at 6:00 AM (90-minute cycles, 15 minutes to fall asleep)
Five cycles back from 6:00 AM is 10:15 PM; six cycles is 8:45 PM. Those two are recommended. The rest of the list is 7:15 PM, 11:45 PM, 1:15 AM, 2:45 AM, and 4:15 AM.
Go to bed at 11:00 PM (100-minute cycles, 20 minutes to fall asleep)
Five cycles forward is 7:40 AM; six is 9:20 AM. Then 11:00 AM, 6:00 AM, 4:20 AM, 2:40 AM, and 1:00 AM.
Sleep length of 7 hours 30 minutes before a 6:00 AM wake
Subtract 7 hours 30 minutes from 6:00 AM to get a bedtime of 10:30 PM. Going to bed at 11:00 PM and sleeping 8 hours 15 minutes lands a wake time of 7:15 AM.