How this calculator works
The chosen-duration method subtracts your requested time asleep and time to fall asleep from the wake time. Cycle methods instead calculate a duration from a first cycle plus repeated later cycles. The table compares all one-to-six-cycle options that fit within a day, so you can see how much sleep each plan actually permits. A 90-minute cycle is only a planning assumption: NHLBI describes cycles commonly restarting every 80 to 100 minutes, with variation through the night. These clock calculations cannot locate a sleep stage or predict how rested you will feel. One or two cycles should not be mistaken for a full night of rest. Times use one local 24-hour clock and ignore daylight saving changes. The result is an estimate for information only and is not medical advice.
Formula
For n assumed cycles, sleep seconds = first-cycle seconds + (n - 1) × later-cycle seconds. Otherwise use the chosen sleep duration. Bedtime = wake time - time asleep - time to fall asleep. The result states whether bedtime falls on the same or previous calendar day.
Worked example
For a 07:00 wake time, five assumed 90-minute cycles allow 7 hours 30 minutes asleep. Adding 15 minutes to fall asleep gives bedtime 23:15 on the previous day. If the first cycle is 80 minutes and later cycles are 100 minutes, five cycles with 20 minutes to fall asleep give 22:40.
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Frequently asked questions
Can I plan eight hours without using cycles?
Yes. Select the chosen-duration method and enter eight hours. The cycle fields disappear and are not used in the calculation.
Why does the table include short sleep plans?
The rows illustrate the arithmetic for different cycle counts. They do not establish adequate sleep needs or recommend restricting sleep.
Will a listed bedtime make me wake outside REM?
No clock-only method can establish that. Sleep staging requires measurement, and real cycle lengths do not repeat with exact timing.