Sleep cycle calculator
What a sleep cycle is
A sleep cycle is the stretch of sleep that moves through lighter sleep, deeper sleep, and dream sleep. People often plan that stretch as 90 minutes. The sleep cycle calculator uses that average on purpose: it adds and subtracts clock time so a bedtime or a wake-up can land at the end of a planned cycle.
This page does not detect where a cycle starts or ends. It keeps one fixed length so the six clock times stay easy to recompute.
Sleep cycle time
Sleep cycle time here is that 90-minute block, repeated. Start from the time in the control. The list runs from 6 cycles down to 1, so the sleep lengths are 9, 7.5, 6, 4.5, 3, and 1.5 hours. The fall-asleep setting is extra minutes around that length. Bedtime cards move earlier by those minutes. Wake-up cards move later.
Sleep clock
A sleep clock on this page is those six times read as bedtimes or wake-ups. It is the same list, not a separate chart of stages.
The settings control starts at 15 minutes, and it accepts 5 to 60 minutes in steps of 5. With that starting value and a bedtime of 11:00 PM, the 5-cycle card is 6:45 AM: 15 minutes to fall asleep, then 7.5 hours. The same offset with a 6:30 AM wake-up puts the 5-cycle bedtime at 10:45 PM. Change the offset and all six cards update on this device.
A small face on each card only marks the length: five and six cycles share one mark, three and four another, and one and two a third. Leave the control on "go to bed at" when the night is the fixed time. When the morning is fixed, the bedtime calculator opens on "wake up at".