Sleep cycle calculator
Find the best time to go to bed or wake up based on 90-minute sleep cycles, so you wake up between two cycles rather than in the middle of deep sleep.
How it works
Sleep unfolds in successive cycles of about 90 minutes, alternating between light sleep, deep sleep and REM sleep. Waking up in the middle of a cycle, especially during deep sleep, often produces a feeling of fatigue even after a full night. This tool calculates bedtimes or wake-up times aligned with the end of a complete cycle, taking into account how long you usually take to fall asleep.
Why does the calculation suggest several times?
Each row corresponds to a different number of complete cycles (3 to 6, i.e. roughly 4h30 to 9h of sleep). Depending on your schedule, you can choose the option closest to your constraints while still aiming for the end of a cycle rather than a round number of hours.
Is the length of a sleep cycle the same for everyone?
No, 90 minutes is an average: depending on the person, age and accumulated fatigue, a cycle can last between 70 and 120 minutes. This calculator gives a useful estimate for planning your nights, but it is not an individual guarantee. This information is provided for guidance only and does not replace the advice of a doctor or a sleep specialist, especially in case of persistent sleep disorders.
The calculation is done entirely in your browser: no data entered is sent to a server.