Calculating your sleep cycles: bedtime and wake-up time
Editorial review in progress.
The French National Institute of Sleep and Vigilance (INSV) describes a first cycle of about 90 minutes, and a night of 3 to 5 cycles. The French Inserm describes 3 to 6 cycles of 60 to 120 minutes. This calculator applies 90 minutes, which is an average, not the length of your night.
The calculation runs in your browser. No data is sent or stored.
Example: waking at 7:00 a.m. and 5 cycles of 90 minutes. 5 × 90 = 450 minutes, i.e. 7 h 30. The calculated bedtime is 23:30 (11:30 p.m.) the night before.
Calculate
Choose the wake-up time you want, or the bedtime. The calculator removes or adds 3, 4, 5 or 6 times 90 minutes. It does not add time to fall asleep: the French Inserm and INSV pages read here do not set one.
A night of 7 h 30 corresponds to 5 × 90 minutes. That does not guarantee five complete cycles: the real length of a cycle varies.
The sleep phases
The French INSV page describes, in order, stage N1 (a few minutes between wakefulness and sleep), stage N2, deep slow-wave sleep, then a first episode of REM sleep after about 1 h 30. The French Inserm describes the same stages: N1, N2, N3 (deep slow-wave sleep), then REM sleep.
The expression “the 5 sleep phases” circulates widely. The two pages read do not count five distinct phases: they describe N1, N2, deep sleep and REM sleep. The French INSV also refers to the Rechtschaffen and Kales classification for the electroencephalogram, without making it a list of five durations to add up.
Over the night, the French INSV indicates that deep slow-wave sleep is plentiful at the start and then becomes scarcer, while REM sleep takes up more room. The French Inserm infographic gives orders of magnitude of sleep time: transition about 4 to 5 %, light slow-wave sleep 45 to 55 %, deep slow-wave sleep 16 to 20 %, REM sleep 20 to 25 %.
Why 90 minutes is an average
The French Inserm writes that a cycle lasts 90 minutes on average in adults, with variations from 60 to 120 minutes, in a report produced with Joëlle Adrien (Science et Santé, 2017). The French Inserm's public page sums up the night as 3 to 6 cycles of 60 to 120 minutes.
The calculator does not know your electroencephalogram. It aligns a clock with an average. To see the phases of a given night, you need a recording, not a subtraction.
This information does not replace the advice of a healthcare professional. This calculation does not measure your sleep.
Frequently asked questions
How many sleep cycles per night?
The French INSV indicates 3 to 5 successive cycles. The French Inserm indicates 3 to 6 cycles. The number depends on the length of the night and the real length of each cycle.
What are the 5 sleep phases?
The French Inserm and INSV pages read for this tool describe stage N1, stage N2, deep slow-wave sleep and REM sleep. They do not publish a list of five phases with a fixed duration for each.
Should you add 15 minutes to fall asleep?
Not in this calculator. The texts read set no single delay. Falling asleep varies from one person to another and from one night to the next.
Sources
Read also
Elio reads the phases of the night, not an average. Elio analyzes duration and phases (light, deep, REM), sleep latency and the regularity of your schedule. It is not a sleep examination. See the Elio band